You mean you're green hand of ERwin or of Databse? If you're good at database, Erwin is a piece of cake. Otherwise I'm afraid it takes some time.
Anyway, Erwin is only a tool, not intelligent enough to design the tables for you. For me, generally I create tables first, draw the ERwin file from the database(Reverse Engineer). How to design the tables depend on how they will be used. Why not publish your requirement here let folks help you. You'll get as good design as possible.
