When you installed Forge, did you make a test world first with the Forge Profile? This will create extra folders you'll need, including the mods folder.
Second, make sure the mods you want are the same version as MC and Forge. You mentioned your using 1.12.2, the mods you want also have to be for 1.12.2.
Third, make sure your using the Forge Profile when you hit the Play button. Forge is actually three mods once run, the three you listed.
You can also use a third party app like MultiMC or CurseForge to run modded MC. These apps make it easier to create Forge Profiles and install mods.