I just bought a Canon 7D SLR with a lens cover, and I took a black photo with many white spots. What happened? I've been a novice for a month, so depressed!

First, determine what your iso is. The higher the iso, the easier it is to produce "noise" as you said. In general, when ISO100,200, this noise is relatively small or almost absent.

Then, it's best to block your viewfinder (that is, the place where your eyes are close to the camera when taking pictures), because light will enter from this place, which will cause you to take pictures that are not pure black. I think the simple and safe way is: choose night and adjust iso, aperture and shutter speed; Then cover the lens, turn off all the indoor lights, put the camera on your chest and take more pictures.