Download the correct OptiFine version from the official OptiFine website
Make sure your Minecraft version matches the OptiFine version
Open the downloaded OptiFine .jar file
Click Install in the OptiFine installer
Open the Minecraft Launcher
Select the OptiFine profile in the launcher
Click Play
If needed, install the required version of Minecraft first
If the .jar file does not open, install Java
Do not use unofficial OptiFine downloads