Long exposure means that you leave the shutter open for a longer time to create effect from clouds or water or moving object. A crowded place could seem empty as people disappear in long exposures when moving, but mostly we use long exposure to isolate a beautiful view and to get the water a bit milky we use long exposure. This is used in waterfall pictures very commonly.
What equipment do we need to perform a long exposure? Two situations give different equipment:
Long exposure during daytime require you to use a ND filter to bring down the light. The ND filter blocks light. Nd filter comes in different strength, blocking more och less light. I use a ND 400 blocking 10 stops. During night time we dont need the ND filter but could leave the camera open for a longer time.
In both cases we need a sturdy tripod to avoid shakes. A remote trigger for the same reason and even if your camera has the MUP (mirror up) we avoid shakes from the fact that the whole camera shakes when the mirror is changing position. If you don't have a remote you can trigger the camera with the self-triggering. Focus on something 1/3 away in the total picture and turn the focus over to manual. When you add the ND filter you will not be able to look through the viewfinder. If you have live view on your camera this could be used instead. I normally take of the camera strap even to avoid the wind to disturb my picture. Here you go: Good light and keep the questions coming.