The SUM function can take a cell range as argument.

You can sum multiple ranges of potentially different sizes by separating them with a coma.

A table column can be easily be used as argument of SUM.
Type
=SUM(.
Select one cell from the column which should be summed.
Press
Ctrl+Space bar, the whole column is selected.
Done
When adding or removing rows from the table the formula remains valid. This is in general not the case without a table.

AVERAGE works similarly to SUM.
AVERAGE on one range

AVERAGE on multiple ranges

AVERAGE on a table
