Forge is basically a Minecraft Mod loader, which means when you start Minecraft then Forge will load your mods.
Hit F3 in Minecraft before you start the procedure listed below and record your FPS–it is on the top line, right after the Minecraft version number
1.) Check to see what version of Minecraft you are playing on BananaSmores with (currently 1.7.2 for me)
2.) Download the Forge mod loader installer for your version of Minecraft (from step 1) at: http://files.minecraftforge.net/
***** Make sure you click the INSTALLER link *****
3.) Doubleclick the installer and choose the defaults, once it’s done Forge is installed.
4.) Doubleclick the Minecraft Icon to launch the game, on the first window that pops up in the lower left corner you will see a Profile. Choose the profile you generally play and then click the Edit Profile button.
5.) Reference the screenshot below, and go down to Use Version and click the down arrow on the right, browse down until you find your version from Step 1 and Forge with the version of Forge you installed in Step 3.
6.) Click the Save Profile button in the lower right and now Forge will be loaded every time you start Minecraft. To verify installation, start Minecraft and at the screen where Minecraft asks to choose Single/Multiplayer you should see Forge listed in the lower right and the version number. If you don’t see Forge listed then Forge is not loaded, go back to Step 5 and make sure your profile updated to the version of Minecraft you are using with the Forge version.
7.) Once that’s done, head over to the Optifine website at: http://optifine.net/downloads.php
8.) Once again find the version of Minecraft you are using, then choose the file with the most recent date. It should be something like: OptiFine 1.7.2 HD U D1
9.) Download the file and put it in your Minecraft/mods folder.
10.) Now all you have to do is start Minecraft and you should see the Forge and also the Optifine listed on the Single/Multiplayer screen.
11.) Hit F3 again and compare your FPS to the FPS you had before you started this procedure. FPS increases vary.