How do i retrive my songs from itunes

Hello, i just bought the shuffle..paid for and installed my first playlist from itunes store...next day i bought another gift certificate....synced those purchases and deleted my first playlist....didn't manually sync it..so....my purchases from the first playlist are not anywhere..there not in my library and i remember a pop up asking me if i wanted to back up my songs...i hit the later button and forgot about it...how do i retrieve the first playlist and what do i have to do to save my purchases...so this does,nt happen again? 50$ worth of music missing....PLEASE HELP!!!!