Legacy 2000, doesn't start

Sudently my Subaru didn't start. I used another's car batery to start my car, it worked, but when I tryed to move the car, it turned off.
Now I can't even take the key out of the ignition.

Some ideas?

When you say "I used another's car batery to start my car, it worked, but when I tryed to move the car, it turned off" do you mean you jumped started it with a battery in parallel with your own battery or that you replaced your original battery with one from another's car?
Your description indicates a loss of battery power and the first thing to do is have your battery load tested. If it fails the load test, replace it. If it passes the load test you'll need to look further into the electrical system.

either battery or a alternator?