If you prefer not to use the vanilla Minecraft launcher, you can use a free program called MultiMC instead.
download & Install
You can visit MultiMC's website and download the software for free. Wherever you unzip the file is where your program will open, it does not require an installer. Once the file is unzipped, open the MultiMC folder and click on the MultiMC.exe program.
Setup your game
Create a New instance
Click on 'Add Instance" in the top left corner of the MultiMC main window.
Choose your version
At the top of the page, you can choose the name for your Minecraft Instance.
Scroll down and choose game version 1.12.2 from the list of Vanilla versions.
Press OK when finished.
Edit Instance
On the main MultiMC page, select your Instance version and choose 'Edit Instance' from the list on the right.
Add Forge
On the version page, click on "Install Forge" from the right menu.
Choose Forge Version
Scroll down the list and choose version 14.23.5.2768. This is the version Tango used to build the mod and we cannot guarantee that other versions will work.
Click OK after you have selected the version.
Add Mods
Click 'Loader Mods' from the left menu. This is where we will add mods.
Select 'Add' on the right to get started.
Navigate to your downloads folder.
You should have the most recent version of Tektopia. Select it, then click 'Open' to add them to MultiMC.
Once Tektopia is shown in the Loader Mods window, you can press close and return to the main MultiMC page.
Open minecraft
Launch Minecraft
Now that Forge and the mods are installed, it's time to launch your game.
With your Instance selected, click on 'Launch' from the right menu.
You can tell that Forge is installed.
The version number will be listed in the lower left.
Once you see this screen, you are ready to get started. Have fun making amazing villages!