A stores a dynamically-typed value. A stores a key-value pair. A stores metainformation about a key.
<g-conf-value> stores one of the value types GConf understands; GConf
uses <g-conf-value> to pass values around because it doesn't know the
type of its values at compile time.
A <g-conf-entry> pairs a relative key name with a value, for example if
the value "10" is stored at the key "/foo/bar/baz", the <g-conf-entry>
will store "baz" and "10".
A <g-conf-meta-info> object holds metainformation about a key, such as
its last modification time and the name of the schema associated with it. You
should rarely if ever need to use <g-conf-meta-info>. (In fact you can't
get the metainfo for a key using the current API.)