Look up the McMMO Wiki site for what the skills are. You get different abilities and bonuses, all of which are detailed in that website. Most of those are highly useful in Noobstown. Also, for more information on a specific skill, do /<skillname> on the chat.

EDIT: The "more info" doesn't work for /mining though. (Maybe because the chat mistakes it for a chat channel, the Mining World channel).

EDIT: They just now fixed the /mining issue! Yay admins!