Hello Bernardhoa - welcome to the forum!
Ya know - there are just innumerable threads/posts that already exist on iCloud - please do a little searching and reading before posting such a redundant question - for a starter try out
THIS THREAD - but basically, iCloud is a means to store your iPad backups/data/etc. on Apple's servers via the web - all is up there in cyberspace; for myself, I'm not using the service yet - there are a lot of questions for those who chose to use (or not) the service - AGAIN, do some searching here, plenty of your questions may have already been addressed; if not, then post back - plenty of great folks here to help - good luck!