math
How do I sum a column of numbers on Apple numbers
iMac 21.5″, macOS 10.15
Take a look at at the Personal Budget template at File > New in your menu.
Row 11 there is defined as a Footer Row so you can put in a very simple formula =SUM(B).
If you are just learning how to enter things in Numbers then be sure to visit Help > Numbers Help in your menu.
SG