How to add different user with different permission for the Database

Question

hi..

i want to create a different user with different permissions..

i have one database..named School Database..

 now what i want is i want the principle with different 

login name and password and the staff with different login name 

and password.. 

and the main thing the principle should have the rights to 

create delete and edit permission and the staff should have 

only the read permission ...

I'm using Sql server 2008 

help me....