In order to get the best Astro Images you need to do several things. You need to take long exposures an you need to take a lot of them.
Most DSLR cameras have a 'Bulb' setting which allows you to expose for an indefinite time. They also have some means of electronic remote control.
DSLR Timers such as the ones below allow you to preset the delay before opening the shutter, how long to expose for, how long before exposures and how many.
Now you can setup the camera and let it take pictures for you!