Step 1: Understanding Night Photography
Wider aperture would make a brighter background, narrow aperture a dimmer background for night photography at least. ISO would mean sensitivity to light. The higher the ISO, the more sensitive it gets to absorbing light. Shutter speed on the other hand would mean the exposure time. How long the shutter would stay open to capture the image.
However, astrophotography is totally different. You need to experiment on some set-up until you reach the desired result.