Download the OptiFine `.jar` file from the official OptiFine website
Make sure you have the correct Minecraft version installed
Install and open the Minecraft version you want to use with OptiFine at least once
Double-click the OptiFine `.jar` file
If the installer does not open, install Java first
Click `Install` in the OptiFine installer
Open the Minecraft Launcher
Select the OptiFine profile
Click `Play`
If you want to use OptiFine with Forge, install Forge first and then place the OptiFine `.jar` file in the `mods` folder
If the game does not launch, verify that the OptiFine version matches your Minecraft version