A userlist can add either a nickname or its mask to a database for reference when a command is said. In this case, i added mask 11 to the database at level 10. Make 11 (not sitting infront of mirc atm, but) looks sort of like:
*!*Shy@mask-A?b?c?.Host.com
This means that any nickname is valid, the ident must match, and the valuable parts of the mask must match. In my experience, this is the most secure mask to use, as it works just as well on a 56k modem (changing ip) as it does with something lik cable. I.E. even if you reconnect to your internet provider, you should still have access.
But the userlist is just a reference point for mIRC. In this occurance, mirc has an on text event. When someone types something in the channel, mirc looks for their name/mask in the user list. So right now say we have the above mask in your user database at level 10. Well if that user were to type something, mirc would look for a match in the database and return the level.
The 10 means that a level 10 and higher can access this command. So in the case of someone joining with:
Shy_and_Quiet!*Shy@mask-A1B2C3.Host.com
You would match *!*Shy@mask-A?b?c?.Host.com because of the wilcards (? = single character, * miltiple or none):
*!*Shy@mask-A?b?c?.Host.com
Shy_and_Quiet!*Shy@mask-A1B2C3.Host.com
So now mirc says "hey, this user is a level 10, this command requires atleast a level 10, let them use this command". From there its just a matter of coding your command.
Hope that helps. >:D
