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If you are porting your application from GConf, most likely you already have a GConf schema. GConf comes with a commandline tool gsettings-schema-convert that can help with the task of converting a GConf schema into an equivalent GSettings schema. The tool is not perfect and may need assistence in some cases.
Example 20. An example for using gsettings-schema-convert
Running gsettings-schema-convert --gconf --xml --schema-id "org.gnome.font-rendering" --output org.gnome.font-rendering.gschema.xml destop_gnome_font_rendering.schemas on the following desktop_gnome_font_rendering.schemas file:
        
<?xml version="1.0"?>
<gconfschemafile>
    <schemalist>
        <schema>
            <key>/schemas/desktop/gnome/font_rendering/dpi</key>
            <applyto>/desktop/gnome/font_rendering/dpi</applyto>
            <owner>gnome</owner>
            <type>int</type>
            <default>96</default>
            <locale name="C">
                <short>DPI</short>
                <long>The resolution used for converting font sizes to pixel sizes, in dots per inch.</long>
            </locale>
        </schema>
    </schemalist>
</gconfschemafile>
produces a org.gnome.font-rendering.gschema.xml file with the following content:
<schemalist>
  <schema id="org.gnome.font-rendering" path="/desktop/gnome/font_rendering/">
    <key name="dpi" type="i">
      <default>96</default>
      <summary>DPI</summary>
      <description>The resolution used for converting font sizes to pixel sizes, in dots per inch.</description>
    </key>
  </schema>
</schemalist>
       GSettings schemas are identified at runtime by their id (as specified
       in the XML source file). It is recommended to use a dotted name as schema
       id, similar in style to a D-Bus bus name, e.g. "org.gnome.SessionManager".
       In cases where the settings are general and not specific to one application,
       the id should not use StudlyCaps, e.g. "org.gnome.font-rendering".
       The filename used for the XML schema source is immaterial, but
       schema compiler expects the files to have the extension
       .gschema.xml. It is recommended to simply
       use the schema id as the filename, followed by this extension,
       e.g. org.gnome.SessionManager.gschema.xml.
      
        The XML source file for your GSettings schema needs to get installed
        into $datadir/glib-2.0/schemas, and needs to be
        compiled into a binary form. At runtime, GSettings looks for compiled
        schemas in the glib-2.0/schemas subdirectories
        of all XDG_DATA_DIRS directories, so if you install
        your schema in a different location, you need to set the
        XDG_DATA_DIRS environment variable appropriately.
      
        Schemas are compiled into binary form by the
        glib-compile-schemas utility.
        GIO provides a glib_compile_schemas
        variable for the schema compiler.
      
        You can ignore all of this by using the provided m4 macros.  To
        do this, add to your configure.ac:
GLIB_GSETTINGS
        The corresponding Makefile.am fragment looks like
        this:
# gsettings_SCHEMAS is a list of all the schemas you want to install gsettings_SCHEMAS = my.app.gschema.xml # include the appropriate makefile rules for schema handling @GSETTINGS_RULES@
        This is not sufficient on its own.  You need to mention what the source
        of the my.app.gschema.xml file is.  If the schema
        file is distributed directly with your project's tarball then a mention
        in EXTRA_DIST is appropriate.  If the schema file is
        generated from another source then you will need the appropriate rule
        for that, plus probably an item in EXTRA_DIST for the
        source files used by that rule.
      
One possible pitfall in doing schema conversion is that the default values in GSettings schemas are parsed by the GVariant parser. This means that strings need to include quotes in the XML. Also note that the types are now specified as GVariant type strings.
<type>string</type>
<default>rgb</default>
        
becomes
<key name="rgba-order" type="s">
  <default>'rgb'</default> <!-- note quotes -->
</key>
        
Another possible complication is that GConf specifies full paths for each key, while a GSettings schema has a 'path' attribute that contains the prefix for all the keys in the schema, and individual keys just have a simple name. So
<key>/schemas/desktop/gnome/font_rendering/antialiasing</key>
        
becomes
<schema id="org.gnome.font" path="/desktop/gnome/font_rendering/">
  <key name="antialiasing" type="s">
        
        Default values can be localized in both GConf and GSettings schemas,
        but GSettings uses gettext for the localization. You can specify
        the gettext domain to use in the gettext-domain
        attribute. Therefore, when converting localized defaults in GConf,
        
<key>/schemas/apps/my_app/font_size</key>
  <locale name="C">
    <default>18</default>
  </locale>
  <locale name="be">
    <default>24</default>
  </locale>
</key>
        
becomes
<schema id="..." gettext-domain="your-domain">
 ...
<key name="font-size" type="i">
  <default l10n="messages" context="font_size">18</default>
</key>
        
        GSettings uses gettext for translation of default values.
        The string that is translated is exactly the string that appears
        inside of the <default> element.  This
        includes the quotation marks that appear around strings.
        Default values must be marked with the l10n
        attribute in the <default> tag, which
        should be set as equal to 'messages' or
        'time' depending on the desired category.  An
        optional translation context can also be specified with the
        context attribute, as in the example.  This
        is usually recommended, since the string "18"
        is not particularly easy to translate without context.  The
        translated version of the default value should be stored in the
        specified gettext-domain.  Care must be taken
        during translation to ensure that all translated values remain
        syntactically valid; mistakes here will cause runtime errors.
      
        GSettings schemas have optional <summary> and
        <description> elements for each key which
        correspond to the <short> and
        <long> elements in the GConf schema and
        will be used in similar ways by a future gsettings-editor, so you
        should use the same conventions for them: The summary is just a short
        label with no punctuation, the description can be one or more complete
        sentences. If multiple paragraphs are desired for the description, the
        paragraphs should be separated by a completely empty line.
      
        Translations for these strings will also be handled
        via gettext, so you should arrange for these strings to be
        extracted into your gettext catalog. One way to do that is to use
        intltool. For that, you use <_summary>
        and <_description> elements in a
        .gschema.xml.in file and use
        @INTLTOOL_XML_NOMERGE_RULE@
        in your Makefile.am to produce the .gschema.xml file. The
        NOMERGE part of the rule instructs intltool
        to extract translatable strings, but not merge the translations
        back into the generated xml file.
      
GSettings is a bit more restrictive about key names than GConf. Key names in GSettings can be at most 32 characters long, and must only consist of lowercase characters, numbers and dashes, with no consecutive dashes. The first character must not be a number or dash, and the last character cannot be '-'.
        If you are using the GConf backend for GSettings during the
        transition, you may want to keep your key names the same they
        were in GConf, so that existing settings in the users GConf
        database are preserved. You can achieve this by using the
        --allow-any-name with the
        glib-compile-schemas schema
        compiler. Note that this option is only meant
        to ease the process of porting your application, allowing parts
        of your application to continue to access GConf and parts to use
        GSettings. By the time you have finished porting your application
        you must ensure that all key names are valid.