Why is there a terminal emulator in the Android App Market?
So you can get direct access to the commandline?
Android is based on Linux, so it's essentially the Linux commandline you'd be accessing here
If you don't know the Linux commandline:
Please note that it'll be a somewhat limited environment - you might need to root your phone to get access to everything, also some commands won't be available, you probably want to install something like Busybox to get a more featureful environment.