Install Minecraft Java Edition
Download and install a shader loader like OptiFine or Iris
Download a shader pack compatible with your Minecraft version
Open Minecraft with the shader loader profile
Go to Options
Go to Video Settings
Open Shaders or Shader Packs
Click Open Shader Pack Folder
Move the downloaded shader pack ZIP file into the folder
Return to Minecraft
Select the shader pack
Apply the changes
Adjust graphics settings if needed