First go to minecraft forge (you can click this) Select The latest forge version. (1.7.10). once you find the right version click Installer Then it will download it. Drag it to your desktop and close all running minecraft windows then open the installer. It should have install to client or if you want to install it to a server you can. Then select the one you want and then click ok. It will install it to your minecraft. Open your launcher again and check to see if you have forge. if you do then go into edit profile open game directory and a folder will open up with all your saves and screen shots and folders for minecraft create a folder called Mods inside of you game diretory then download the mod you want make sure to see if it requires anything then drag the mod into your mods folder and launch your minecraft it should say in the bottom left cornor how many mods you have. then you can play with the mod you want.

Hope this was helpful if you still have trouble I am making a video so you can follow it.