How to install Minecraft Forge
1.Download the recommended installer for 1.7 from the Minecraft Forge API
2. Open the .jar file you have just downloaded, make sure ‘Install client’ is selected and click OK. Once this has finished you will see a success message.
3. Launch Minecraft and select the Forge profile then click Play.
4. You should now see some Minecraft Forge text in the lower left hand corner and a Mods button below Multiplayer.
If so, congratulations, you have successfully installed Minecraft Forge!