This question is somewhat unrelated to Minehut, however you can install shaders by going to https://optifine.net/downloads and downloading the latest version of Optifine (1.14.4) and installing it, then downloading a shader pack from any various source and placing it into your shaders folder inside your .minecraft.
Note: The latest version of Optifine with shaders implemented is 1.14.4, the preview versions for 1.15.2 do not yet have the ability to load shaders, and with 1.15.2 being the version of paper which Minehut runs on, its likely that you will not be able to join many public servers unless they run ProtocolSupport or ViaVersion.