Having good backups are something I have preached for years!! This topic became even more important in the wake of the disasters we have seen and experienced this last year. Apple has made basic backup to an external drive very easy with their Time Machine software. Time Machine is great because it gives you the ability to recover a document you may have accidentally deleted. However, this should only be the beginning of your backup strategy. There is a standing rule that a 3-2-1 strategy for your data is a must. This means that you have two local copies of all your data (i.e. your main computer and an attached external drive) and one backup off site or in the cloud.
Many people have the mistaken impression that Apple's iCloud also functions as a back up for your computer - it does not. iCloud is perfect for synchronizing your calendars, contacts, reminders, and notes between devices and as long as you are using iCloud Photos, it can also creates a backup of your Photos library. If you use an iOS device, iCloud is also perfect for creating a back up of your iPad or iPhone. But iCloud is not a backup for your computer!
To truly create an offsite backup of your computer it's necessary to use a third-party cloud software such as Backblaze or use a second external drive that you swap in and out and store somewhere other than the area you live in. Either of these choices have advantages and disadvantage - see the comparison chart below for more information.