The iTunes 'cloud' facilities are quite separate from iCloud and don't even have to have the samew login.
'iTunes in the Cloud' enables you to download songs (and now movies) purchased on one of your devices onto any other of your devices. This comes at no cost as it doesn't occupy any further server space (the songs already being there - you can't do this with songs which have been removed from the Store).
'iTunes Match' enables you to upload songs you've obtained from other sources to the server, so that they can be downloaded to other devices. This costs $24.99/£21.99 per year, limit 25,000 songs (purchases do not count towards this limit). This is not part of the 5GB free storage in iCloud.
You do all this in iTunes, not in iCloud.