backing up my mac

How do I back up my MacBook Pro to iCloud?

iCloud cannot be used for that purpose.

What does iCloud back up? - Apple Support

Noteworthy excerpt:

• Use Time Machine to back up or restore your Mac.

It's supposed to be automatic. How much are you paying for it, and how much max storage? It may not be enough.

Add your Desktop and Documents files to iCloud Drive - Apple Support

I'd recommend using Time Machine or cloning software. It would be much better if you need to recover.

"On the cloud" is great for sharing photos, but is not a viable backup solution for everything you have. The stuff is not under your control, and is subject to sloppy handling, arbitrary changes in policy, theft, data loss, and bankruptcy of the company that holds it. It can easily take three days to restore it at ordinary Internet speeds.

If you do not have a recent local, disk-based backup, your computer is like a ticking Time bomb. You are only one disk failure away from losing EVERYTHING! Drives do not last forever. It is not a question of IF it will fail, only WHEN it will fail.

If you are using another direct-to-disk backup method that you prefer, and you currently have a recent disk-based backup, that is great. If not, you should consider using Built-in Time Machine. Take steps to acquire an external drive as soon as possible. If you buy one, a drive 2 to 3 times or larger than your boot drive is preferable for long term trouble-free operation. Do not pay extra for a drive that is fast.  (You can get by for a while with a "found" smaller drive if necessary, but it will eventually become annoying).

Attach your external drive and use

System preferences > Time machine ...

How to use Time Machine to Backup or Restore your Mac:

Back up your Mac with Time Machine - Apple Support