This tutorial assumes that you already have Minecraft installed.

Step 1: Step 1: Install 1.12.2

Most mod packs for Minecraft run off of 1.12.2. The base level for Forge (the program we will be using to manage mods) will require an installation of 1.12.2. To install a new version of Minecraft...

Launch the Minecraft Launcher and click the Installations tab as shown in the first image
Click on New as shown in the second image
Under Version, select 1.12.2 as shown in the third image
Name your installation and hit create. You should be back on the second screen with the new installation
Hover over that installation and hit play. The game will automatically download the required files.
Exit Minecraft

Step 2: Step 2: Install Forge

The forge installation is rather painless.

Go to the Forge website and click on Windows Installer as shown in the first image.
This will lead you to a website that looks like the second image. It does not show for me because I am using an Adblocker. However, usually some ad shows up in the whitespace prompting you to download something. DO NOT DOWNLOAD IT. It is not required for Forge and likely contains a virus if downloaded.
Wait 6 seconds or so (there is a timer in the upper right hand corner highlighted by the red box in the second image). Then a Skip button will pop up. Click it.
A download will start
Run the downloaded file and an installer window will show up.
Select "install client" and follow the instructions on the installer. (default directory paths are fine)

Step 3: Step 3: Running Forge

Open the Minecraft Launcher Again
Under installations there should be a new one called forge
Hover over it and hit play
Allow the game to install the necessary components.

Step 4: Step 4: Installing Mods With Forge

In your file explorer, click on the top bar (highlighted in the first image) and type in %appdata%
Open the .minecraft folder
Place the downloaded mod jar files into the mods folder
Relaunch Minecraft with Forge