Movement "Space is big. Really big! You've no idea how vastly, hugely, mind-bogglingly big it is! I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." Douglas Adams, The Hitchhiker's Guide to the Galaxy

One thing that will be come clear when using Celestia is the enormous range of scale between the smallest and largest structures. In Celestia, human built spacecraft are at the low end of the size scale. Galaxies occupy the top of the range; at up to 100,000 light years across, they're roughly 10^19 times bigger than the smallest objects. This makes navigating in Celestia a little less straightforward than in other 3D applications.

Looking Around
To rotate your point of view, simple drag the mouse across the view window. In the Windows version of Celestia, the cursor will disappear allowing you to rotate as much as you like without being limited by the edges of the screen.