Install Minecraft Java Edition
Install the correct version of Java if needed
Install Fabric or Forge for your Minecraft version
Download and install Iris or OptiFine
Download a shader pack compatible with your Minecraft version
Open Minecraft and launch the Iris or OptiFine profile
Go to Options
Open Video Settings
Open Shaders
Open the shader packs folder
Move the downloaded shader pack file into the folder
Return to Minecraft
Select the shader pack
Click Done
Adjust shader settings if needed
Restart Minecraft if the shader does not load
Lower graphics settings if performance is poor