How use gem Cancan on Rails

I have read a lot of website tutorial Cancan gem, but I can't understand
I want to create, edit role, and add user to role. config premiss for
role. etc...

You are probably better going with the cancancan gem which follows on
from cancan. Instructions for using it can be found at [1]. If there
is anything there you do not understand then come back and ask
specific questions.