Most iOS users will be familiar with iCloud by now and would be using it in some capacity. But since you only get 5GB free, you’ll want to manage your storage.
Plenty of apps update their data to iCloud, but you can manage each individually. Head to the iCloud option in the settings app, then “storage and backup”. Then, click on (in my case) “Pat’s iPad” where you can monitor your backups.
There, you can choose which apps you want to update to iCloud. You can turn them on and off at any time.