Sums question...

I have a simple question: I want the sum of the numbers in 2 columns to appear in a third.

For example: I want E1 to show the sum of inputs in C1 and D1. But for every row individually. I know how to do this for each individual row, (basically, E1 = C1 + D1) but it should be unnecessary to program each row separately. I have set up a test sheet with some inputs.

What I want is to be able to just program the E column to show results of the sum of C column and D column. Like this:

C D E
2 3 5
3 4 7

Somebody suggested that I could input the fomula =SUM(C:D). I select the E column and input that formula, but I get an error message. It gets worse, the error message says: "That formula is incorrect, do you want to say =SUM (C:D)? Okay?" If I select the E column and dbl click the first E cell and input that formula I get a totally absurd number. I think what it's trying to do is add all the numbers in ALL the rows in the C and D columns and putting the result in the E1 cell.

Can Excel do what I want, and how? Thanx,

Ken

Excel v11.2.3
Mac G4 DP 1.25 GHz,
1.25 G RAM,
Radeon 9800 128 MB VRAM,
OSX 10.4.9

Thanx, that worked. The "little black box" was sure hard to find. I would never have thought of that!