Stellarium is a free planetarium software program that can be used in a wide range of amateur astronomy observing and astrophotography applications. Find the location of stars, planets and deep sky objects, fast forward or reverse time, zoom in and out, find comets, and much, much more.
Stellarium is the program I show in nearly all of my YouTube videos. It is easy to use, and incredibly powerful. You can download it for PC, Mac or Linux based systems at stellarium.org
I've also created some "how to use" Stellarium videos - at the moment you can find them in my Stellarium playlist on YouTube.