2009 chevy cobalt LT quit

Your saying the starter motor won't even crank the engine? Make sure battery has a full charge and connections all good. If battery is down, use a charger and get it charged up. You can't do any testing if battery is down. If battery was down, make sure charging system is working ok? Check voltage at fuses, use a test lite, just trying to see if you have voltage to fuse boxes. Some fuses are hot all the time, some go hot with the key on, check them both ways. Any applicable trouble codes? I've been talking about voltage circuits, but, grounds are important, also. Battery ground--engine ground--chassis ground--whatever.

Well, my radio is working, lights are working, amp is working, heater and car charger is working, but I'll try charging my battery

You can use digital multimeter across battery posts, everything off, the generic spec for a full charge is 12.6 volts, if it gets much under that, charge it. With meter across battery posts, have helper turn key to crank position, note the meter reading, Does it stay the same, does the reading drop? If it drops, how far does it drop? Usually it shouldn't drop below 9 volts, that spec is generic. On some vehicles, the info says it shouldn't drop below 10 volts, but, you get the idea. If the reading drops down close to zero, that isn't going to work. Just my opinion.