How do I restore my iTunes library and playlists

I will try this. I normally can do this. But I had to restore my computer back to factory and the external drive has it on there but it won't transfer the files. I also transferred my files onto a cd and the computer doesn't recognize the cd for some reason. I truly appreciate what help you offer. I am going now to try what you just suggested. Oh and I couldn't retrieve my songs that I purchased from the store by going back to the store. Thanks again. If I can get this to work, I will let you know.

I only got part of my songs and the last few songs I purchased, I cannot retrieve. I go to store and it says they have all been downloaded. I guess I just can't get the concept of all of this. I always have but this time iTunes has me beat