Select your data, eg: A2:N1000
Click Data-Conditional Formatting - New Rules
Select "Use a formula ..."
If your condition is, say, the value in column G equals 100, enter this formula in the formula box and then format as desired:
=$G2=100
Notice that I used the 2nd row in G2 because that was the 1st row of data selected above, ie A2:N1000. You also need to put a $ in front of G2 so the rule doesn't move across columns.