The code looks like this:

sub Sum_of_two_cells()
msgbox range("a1").value + range("b1").value
end sub

You can use the Control Toolbox on the Visual Basic toolbar to assign
the macro to a button; I prefer to click (on the Excel menu) View
Toolbars Forms and use the command button from that toolbar.

Good luck with it!
Dave O
Eschew obfuscation