Is this honestly needed beyond what is posted? if you don't know what a human is.. look in the mirror. if you don't know what a human with powers is.. go read marvel comics or DC universe comics.. or watch shows by either!
Humans have evolved to the point where many are beginning to obtain powers and most, if not all, can see spirits even if they can't do anything about them.
Humans Powers and Fullbring are as widely unique as a shinigami's Zanpaktou shape is changed. There is probably even fewer limits since the way a human's powers would manifest could be through anything unlike Shinigami's having to have Zanpaktou.
Second Powers vs Fullbring
Having Fullbring doesn't nessicarily make you stronger. There are no extra boosts for it and you can't use your normal powers while wielding a fullbring and it's abilities. The only real difference is a fullbring gives you an object much like a Bount's doll and gives YOU powers instead of the Doll keeping the powers. It's basically there for RP purpose..and doesn't make any difference on your humans total power potential. With or Without it you could still be 2-2 tier and fight on par with 2-2's that are at their full power. (Strengths and weaknesses would apply and make the battle turn out this way or that..but you get my point )
However.. A second stage of powers for a human enhances the power that is already there. Unlike Fullbring you would get boosts for it though..making this debatably better if it comes down to an opponent your powers are already good against and you need that extra jump in power. it increases all of your natural primary stage powers to new heights and new limits. making it in some cases and some ways more superior to fullbring. But unlike Fullbring you can't get an entirely new set of powers that don't match your primary powers from Second stage.
Hyper Mode - This is the equivalent to Quincy Final Form, Shinigami's Ultimate Release, Full Hollow Form, and Vasto Lorde. This is the highest absolute maximum output of a humans powers..this is as close to a god-like state that any human can attain..the only problem is..it only lasts a short time. The human soul is capable of such power but the human body is not ment to handle it. This is very taxing..putting one into fatigue state upon reaching the time limit of this ability. This is basically a humans third and final stage of power.
Blur - This is the human equivalent of Shinigami's shunpo. They mastered this technique to keep up with the spiritual beings.
Airwalk - In case it wasn't clear, most humans can't airwalk. The ones that can use an ability that does it for them. Or uses the Floater Device. The only exception is when using fullbring, as it does allow it.