Optifine is a mod that adds more graphic options to the Minecraft game, thanks to the way you configure your graphic options, to have better performance in the game improving the FPS, so that you will not jerk the game if you have an old PC.
It also has support for installing high-resolution textures in HD, so you do not get any errors when you install Textures Pack HD

How to download and install Optifine for Minecraft 1.12.2

1- Download and install in the following link: Minecraft Forge 1.12.2
2- Download Optifine 1.12.2
3- Go to the Windows Start button, then Run (if not, press ‘Windows’ + ‘R’) and type %appdata%
4- Open the .minecraft folder and then the mods folder
5- Add the downloaded Optifine file inside the mods folder
6- You will already have installed the Optifine 1.12.2

Download Optifine for Minecraft 1.12.2