The SCHEMA and KEY arguments are required for most commands to specify the schema id and the name of the key to operate on. The schema id may optionally have a :PATH suffix. Specifying the path is only needed if the schema does not have a fixed path.
When setting a key, you also need specify a VALUE The format for the value is that of a serialized GVariant, so e.g. a string must include explicit quotes: "'foo'". This format is also used when printing out values.
Note that gsettings needs a D-Bus session bus connection to write changes to the dconf database.