First of all I would suggest you to get a copy of the books online .. or the Holy Book as I call it ...
then read up on following
1/ Which table do I use for logging in as an admisnitrator?
You cannot log in as administrator using some table ... u will have to use sql server authentication or windows integrated authentication.
2/ I need to see total logged in users at the database?
sysprocesses or sp_who, sp_who2
3/ I need to drop s someones connection to db?
4/ I need to add new users?
5/ modify ones privileges?
grant , deny , revoke
6/ delete user?