GSettings and GConf are two similar -in concept- classes that keep information about keys and their types in schemas and provides a mechanism for Gnome Applications to store their settings.
There are some differences in the approach to schemas. GConf installs the schemas into the database and has API to handle schema information. GSettings on the other hand assumes that an application knows its own schemas, and does not provide API to handle schema information at runtime. GSettings is also more strict about requiring a schema whenever you want to read or write a key. To deal with more free-form information that would appear in schema-less entries in GConf, GSettings allows for schemas to be ‘relocatable’.
One of the major goals of Gnome 3 was to port all applications from GConf to GSettings. Last update shows that we are almost there, with most of the Gnome modules to have been already migrated to the new class.
One module that earned lots of functionality by this, was Gnome-Shell-Extensions, where on version three point four gained access to GSettings and can “communicate” with applications.