How to add to cells and return the result inthe third cell in excel?

Question

say, i have the following data

A  B  C
3  5  
4  8  
5  9  
6  0  
7  6  
8  3  
9  4  

How can i add two cells from each line and put the result in the cloumn C, the result should look like this..

A  B  C
3  5  8
4  8  12
5  9  14
6  0  6
7  6  13
8  3  11
9  4  13

thank you

Answer 1

write: =(A1 + B1) in cell C1.
then select the cell, there's a little square in one of the corners, click it and drag down.

Answer 2

In cell C1 (assuming that 3,5 line is row 1), enter =a1+b1 and hit ENTER.

Then click in that cell, grab the bottom right corner of it and drag/extend it to the seventh row.