Find or borrow a voltmeter from autozone or someone.
There are two leads. Positive (red) and negative (black).
Start the engine.
Place the black lead on a ground...(strut tower bolt or any metal chassis part under the hood)
Then place the red lead on the bolt on the alternator that holds the cable that runs to the positive battery terminal.
Check the voltage. Anything over 12 and up to 14 is ok. It means your alternator is sending a charge to your battery.