type: dot -Tps filename.dot -o outfile.ps
If you want to use the dot renderer. There are alternatives like neato and twopi. If graphiz isn't in your path, figure out where it is installed and run it from there.
You can change the output format by varying the value after -T and choosing an appropriate filename extension after -o.
If you're using windows, check out the installed tool called GVEdit, it makes the whole process slightly easier.