Just hit the = sign in the space where you want the sum
then type SUM(
then click on the other worksheet and select the cells you want to add up... hold down CTRL to select multiple cells, or SHIFT to select all within.
then type ) and hit ENTER... should give you a formula that looks kinda like this
=SUM('WS3'!A3:A5)
which mean on worksheet WS3 add up all in A3, A4 and A5...
change to what you need
