The only "commands" available in Jass are the functions you can call. A list of all the native (built-in) functions can be found here: http://jass.sourceforge.net/doc/api/common_j-functions.shtml You can also use my editor found in the tools section which has a quick searchable list of all the functions in common.j and blizzard.j.
I don't know of any reference which actually has a description of each function.
To change a player's gold, you should use SetPlayerState.