Hi arzoo,After U create repository add folder to U'r repository in Repository manager.U can do this by using the menu item Add Folder.Then come to Designer to create mapings.Designer consists of 5 different tools Source Analyzer,Warehouse Designer,mapping Designer,Mapletdesigner,Transformation Developer.
U have to create mapings in maping designer and then save it in to repository.
Regards
Ravi Yanumula