you need a multimeter and read input to battery from alt. should read about 13-15 volts, start the car and put multimeter on bat, neg to black wire pos to red wire. while car is running check voltage. if its below 13 volts take the alt off and have a shop or autzone run a test check. but first check battery voltage car not running should be 12 volts or better if not battery might be the only problem.
Take to autopart shop and have alternator tested. First, use voltmeter on battery to get a read. Then attach black end of voltmeter to black on battery and red from voltmeter to red wire coming off of alternator. Do this with car turned off. If the second read is about 0 then the fusible link is burnt out and replace it.