I see a lot of screenshots that use fantastic shaders. I mainly play modpacks, and am unsure how to get it to work there. Is there a guide on getting it working? As a followup, are there specific texture packs that tend to look extra nice with shaders?
I'm sure there are a few guides for specific shaders, but I don't think there is a guide that is more general covering them all. I would just pick one that looks good to you and follow it's installation instructions to install it. Make sure it is compatible with the Minecraft version you're running and with your hardware. You'll want a fairly beefy PC with a dedicated graphics card. If your FPS is already barely tolerable then don't even try running shaders.
There are a few resource packs that recommend certain shaders, but most all of them will work with and look better with shaders. Usually their official page will recommend a specific shader. For example the forum page for Conquest, if you scroll down to the 'Mod Support' heading, you will see a couple shaders listed.
Shaders are simple in the new update, download optifine for 1.11.2 or whatever and get a shaderpack(also 1.11.2) and run minecraft with optifine installed go to video settings \shaderlopen shadersfolder and drop your desired shader in and viola( I believe the newest version of optifine comes it's a few shaders automatically like SUES and sildurs