roles v/s entitlements

hi team,

can any one tell us what is the difference between roles and entitlements ,

in what way they are different and their advantages

we are also interested in knowing their use case in provisioing

actually we need to provision user data along with roles ,how can this be achieved

right now we are able to provision user data but not roles,we follow process form,process definition  in the web service connector

how can we provision roles in process form and also to the target

thanks in advance,

kishore