Install Minecraft Java Edition
Install Fabric or Forge
Download and install Iris Shaders or OptiFine
Download a shader pack
Open the Minecraft launcher
Select the Fabric, Forge, or OptiFine profile
Launch Minecraft
Go to Options
Go to Video Settings
Open Shaders
Click Shader Packs Folder
Move the shader pack ZIP file into the folder
Return to Minecraft
Select the shader pack
Click Done
Adjust shader settings if needed