Regarding the user grouping

I am new to the unix server.
My question is:
i have 10 users
a
b
c
d
e
f
g
h
i
j

Among the 10 5 users are (normal) user and remainging 5 users are (qad) users
How can i sepearte this one?
How can i give the dlc access rights?

Please provide the clear cut idea.