What is backup?
In my mind backup means duplicating your data ie. Documents, photos, bookkeeping data
Your data is usually stored on a hard drive which can stop working at any moment, get stolen, infected by viruses or ambushed by ransomware.
What to backup?
Recommend to backup own generated data eg. Documents, spreadsheets, bookkeeping data, pictures and videos.
Programs can be retrieved from source media and settings be recreated.
External drive, cloud services.
Depending on the importance of your data a rotating off-site backup.
Ask yourself: If I lose this data what will be the impact? Will your business go down? How important is your captured memories?
Then decide how much do you need to spend to preserve your data.