Not sure if you have a specific question, but you essentially create achievements online (at
mogade.com), which will generate achievement ids.
Then, in the game, when an achievement is earned (which is completely up to you to determine), you call:
AchievementEarned(ACHIEVEMENT_ID, "USERNAME", callback);
You can use
GetEarnedAchievements("USERNAME", callback);
to see what the user has already earned.
There isn't much more than this. I always wanted to expand the feature...display achievements on websites...and let people compete or rank based on achievements, but meh, never got to it.
Karl