It's not for a beginner.
Bands and chains "deload" at the bottom, so they're harder/heavier at the top of the lift wher eyou're strongest and lighter at the bottom where you're weakest. So say you can't make a 10lb increase in the gym anymore since you're an advanced lifter and jumping from a 600 squat to a 610 squat in a week is a bit difficult.. You put the bands on and maybe you can get it to 610 at the top, but only like.. 602 at the bottom. Then, when you try 610 again, since the bottom is just that much stronger, it's a bit easier for you to do the 610 without getting stuck.
Bands also have the added benefit of accelerating the bar during the eccentric portion of the lift, allowing you to utilize the stretch-reflex and explode more out of the bottom.. great for dynamic training.
BUT.. for a beginner, all of this is unnecessary.