Minecraft is a sandbox video game. Sandbox means it is similar to kids playing in a 'sandbox' where they build and tear things down.
You can install different versions of Minecraft Forge and Minecraft Mods without uninstalling previous Forge or Minecraft.
The Best Minecraft Forge to Install
Minecraft Forge Version 1.7.10 is the most popular Forge with the most Mods
There are two things you need to do before you can install mods.