How do I format several cells together

I am trying to make a bank log. how do I get several cells to format together and the carry on to the next set, so I can keep goin?

Select a vertical cell range (or click on column header(s) to select entire column(s)) and Format Numbers (Ctrl+1).

I need to know how to to do like k3-k7=sum

=K3-K7

And maybe read a Calc Guide English documentation | LibreOffice Documentation - Your documentation for LibreOffice