Homework? Interview?
Really, this is basic theory. Did you try looking in Books Online, perhaps under 'Function' and 'Stored Procedure'. Or even go and look at computer science theory for the difference between a function and a procedure. Maybe start with wikipedia
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
We stand on the bridge and no one may pass