take it to any auto parts store they will test it for free
If it is broken, cracked, frayed, or stretched so much it cannot be tightened.
First start the car then pull off the positive on the battery if the car dies than you need a new alternator if the car keeps running u may need a new battery. A word of caution, testing an alternator that way can cause damage to the alternator. The alternator needs power to make power unlike the old generators from the past.
In the alternator Needs new Alternator if it's bad
More likely the bearings in your alternator wearing out. Get a new alternator.
the regulator in your alternator must be in trouble remove the alternator and take it to an alternator repair shop or fit a new alternator
Does it crank over fine?
It may be that you need a new alternator.
The the alternator is defective.
your alternator is not charging your battery..u need to get a new alternator
your battery needs to be charged first with a car battery charger then start the car and see if the alt/battery light is on if it is on then you probably have alternator problems if the battery does not charge enough to start the car then get a new battery first a good indication of how the alternator is working is to check the voltage at the battery with the engine running if it is between 13.6v and 14.4v then it should be OK if it is below it then the alternator needs to be replaced or repaired if it is above then the same apply as too high a charge will damage your battery in the long run
Needs new alternator.
The engine needs compression, fuel and spark to run, you are missing one of those.