I know it was already answered, but I'd like to make it a simpler process for the players that have garbage internet like me.
(If I'm incorrect in some parts here, I'll just tell ya that I haven't done this in a while)
- Make sure you have the
standard launcher and not a second party launcher. If you already have the launcher, ignore this step.
- Go
here
- Download the latest version (1.13 in this case)
- Open the launcher and run the Optifine software
- Do what it says and it'll integrate itself in with the .minecraft files.
- Restart your launcher and you'll have it.
- To install shaders and whatever (it'll eat up your resources unless you have a damn good computer), go to any reputable shader site and install them to your .optifine file.
- To activate these shaders, go to the menu in your settings and click on the one you downloaded. It should apply the same way resource packs do.