Please help with Google Sheet

[brannsiu]

I have zero knowledge with Google Sheet or Excel
and I have downloaded some template online

It's template of business invoice. I'd like to add "Amount Paid" and "Amount Due"

i.e Amount Due=Total Amount - Amount Paid

But most of the template have missed this part.

How to do it by myself??

 

[Alabalcho]

You write a formula like

=A5-A6

where "A5" is the cell containing "total amount", and "A6" is the cell containing "amount paid". You write this formula in the cell where you want to hold "amount due".

I think you have to start with something more "basic", like how a spreadsheet works. Jumping straight into templates is not for absolute beginners.