I've started modding Skyrim but have no idea how to install an ENB. I've installed Skyrim High-Res DLC and the High-Res Patch, SkyUI, Enhanced Blood Textures and a couple other stuff but have no idea how to install Realvision.

I have the Skyrim Script Extender, LOOT, Nexus Mod Manager and Mod Organiser and I was wondering how I could make it work

Realvision has detailed instructions on the description page: http://www.nexusmods.com/skyrim/mods/30936/?

Normally it involves downloading the main ENBseries files (currently v0.254), copying the files to the Skyrim folder (not the Data folder), downloading the preset (in this case Realvision) and then copy those files also to the Skyrim folder, if necessary overwriting the v0.254 files.

There are also other settings that must be in place, such as turning off AF and AA in the Skyrim launcher. You'll find it all in the Realvision instructions.