Think of ENB as a pair of sunglasses. First, there is the vanilla Skyrim world as Bethesda intended it to look. Then you have dozens of mods that add hi-res textures. Vanilla is 512 resolution, hi-res is 1024, and some retexture mods even go as far as 2048 (which isn't advisable unless you have a really high end system). Everything in gaming is basically a mesh/wire frame with a "skin" applied over the top, or texture. More detailed textures = more eye candy. There are all kinds of texture mods for faces, caves, clutter items, etc. Then you have lighting overhauls, which add more realistic lighting to the game. These add a bit more depth and realism to those texture mods above. I suppose you could lump the water and weather mods like Climates of Tamriel into this category as well. I'm sure someone will be along shortly with a "but technically..." comment, but whatever. Point being, good lighting adds additional depth to the textures. ENB is a filter that goes over the top of all that. ENB can add nifty eye candy like DoF (depth of field) that makes far away things blurry and out of focus, while objects closer to you remain sharp and in focus...kind of like a camera lens. There's lens flares, more enhanced lighting, sharpness filters, color saturation, etc. My personal opinion is that ENBs are definitely not for the novice modder. The instructions included are often missing steps that will lead to an improperly installed ENB that looks like crap and has unnecessary performance problems. Even a properly installed ENB will drop your FPS enough to make you question if it's really worth it. There are a ton of settings that can be tweaked, but again, unless you really understand how all of it works, you could be hurting more than helping.