Carbonite is online backup only, so it doesn't really work well for local backups or backups to external drives. You'll still have to handle that yourself. You can try Carbonite for free for 15 days, but after that you'll need to pay up $60/yr to back up one computer with their Home plan, $100/yr to back up one computer with their Home Plus plan, and $150/ur to back up one computer with their Home Premium plan. You can read more about Carbonite's plans and pricing here.
For this software, you just need to copy the YouTube link and paste it directly into the box that’s labeled for the link. Then you get to choose the format that you want to download it into. You’re going to need to download their specific software in order to be able to download, but then you just have to click to download, and you’re all set. It really is just that easy. You can even tell it to download multiple URLs at the same time, so you can fill in everything you want to download and tell it to start while you head off to do other things.
Many services also offer a feature called versioning. This saves incremental changes you make to files as recoverable snapshots of the file. It's useful in case you need to get back information from an earlier version or if your latest file save becomes corrupted. Services vary widely in how many versions they keep and how long they're saved. Best-in-class services, such as SOS Online Backup and SpiderOak ONE keep an unlimited number of file versions forever.