Step 1: Go to minecraftforge.net

Step 2: Then click releases

Step 3: Then find the most recent version for 1.6.2

Step 4: Then download the installer

Step 5: Run the installer and select the way you are trying to install;

Step 6: Download the mod you are trying to install

Step 7: Follow the mods instructions (ex: Place mod in mods folder etc etc)

Step 8: Run the launcher

Step 9: Select the "Forge" profile

Step 10: Play!

If this does not work please check how you installed it or what the versions are and make sure they all match