First of all get the battery charged and tested. A completely dead battery can keep the alternator from charging. If the battery tests bad after charging, replace it, then test the alternator. You may only need a new battery.
Once the battery is qualified, you need a voltmeter to test the alternator. With the eingine running at about 2000 RPM (that would be gently reved up) and all electrical accessories off, you should have a voltage reading of about 14.5 volts. It may be a bit lower if the battery is not fully charged (a new battery may not be fully charged).
If the alternator isn't working you will have nearly the same voltage as with the engine off (about 12.5 volts).
Bdfore condeming the alternator if the voltage reading is low, check the mega fuse in line between the battery and the alternator. Also check the belt to make sure the tensioner is holding tension so it isn't slipping.
I hope this helps.
