Download and run the new Minecraft launcher at least once.
Download the latest version of Minecraft Forge API installer, choose the installer option.
Run the downloaded jar file. It will open a menu as shown below:
Press OK, and this will appear:
Open the Minecraft Launcher and select the new Forge profile
Enter your username and password and launch the game at least once.
Minecraft Forge will now have generated its folders in %APPDATA%/.minecraft. Place mods into your %APPDATA%/.minecraft/mods folder as you have in the past.
Run from the Minecraft launcher through the Forge profile and profit?!?!
For Windows users, you just have to run install.cmd. If you’re on linux, you need to copy files and apply patch manually for now, A install.sh for linux users too is on the way.
Credits: The Minecraft Team