Excel 2010 formules et $

Translation of the original:

Hello,
 
In a formula, when I want to put the $ signs, the cell gets gray and turns off.
 
Example: L1C1 + L2C2 = 3
         $L1C1 + $L2C2 = the excel formula contains an error.
 
 
In the same way, I can not extend the formulas. Indeed, when I extend them, they are copied exactly in the same way and not according to the cells.
 
I do not know if I was clear ...
 
Thank you for your help

Do you mean  that your formula is "=L1+C1 +L2+C2"

L1C1 isn't referring to a cell?

Or are you trying to multiple L1 and C1?

In which case "=L1*C1 +L2*C2" should work.