If you are not using Minecraft Forge, you will need to download the Non-Forge Edition of ShadersModCore. Click here to visit the download page.
However the Non-Forge Edition jar is actually an installer and the ShadersModCore jar is bundled inside it:
ShadersModeCore jar
and extract the jar to your versioned mods folder (eg. for Minecraft 1.8 extract to .minecraft/mods/1.8/
ShadersModCore
tweak automatically.