What are the benefits of iCloud and how can I use it on my MacBook Pro?

Here is one explanation of the benefits (from Apple at the site iCloud+ - Apple ):

Also, note that iCloud isn't just one service. It includes the ability to sync data with iCloud and with your other Apple devices (e.g., iPhone, iPad, etc) if you choose. You can make that choice for each device and for each type of data (e.g., Contacts, Photos, Files, etc).

I use iCloud to sync data on my Mac (Photos, Contacts, Notes, Calendars, Safari, etc) with my iPhone and iPad so that I can access the same data from all of my devices. I don't turn on the Optimize Storage options for Files and for Photos on my Mac; because of that, I have a local copy of those things on my Mac at all times and can use Time Machine to backup to an external drive. If both my Mac and my external drive were ever lost (fire, theft, etc) at the same time, my data would still be recoverable.

Another option is to turn on those Optimize Storage options if your local storage on your Mac is too small for the data that you have; with that option on, your Mac can access data from iCloud as needed but free up some storage space when you aren't actively using some of that data.

Also see: Set up iCloud Drive - Apple Support

and

Set up and use iCloud Photos - Apple Support

and

Set up iCloud for Contacts on all your devices - Apple Support

and

iCloud User Guide - Apple Support