In the hobbit film when denying the darkness in dongle dur saurman talks about a man who calls him self a necromancer (sauron), most likely a socerer? or something along those lines implying that men can learn magic?
Apparently they can. Some of the Nazgul were sorcerers before they became wraiths, and the Mouth of Sauron also knew sorcery. Likewise Gandalf tried to open the doors of Moria with the spells of Elves, Men, and Orcs. But the magical arts don't come naturally to Men, so they have to turn to a Vala or Maia -- usually Morgoth or Sauron -- to gain this ability. Note that the Valar are generally not in the habit of giving mortals this power.
Apparently they can. Some of the Nazgul were sorcerers before they became wraiths, and the Mouth of Sauron also knew sorcery. Likewise Gandalf tried to open the doors of Moria with the spells of Elves, Men, and Orcs. But the magical arts don't come naturally to Men, so they have to turn to a Vala or Maia -- usually Morgoth or Sauron -- to gain this ability. Note that the Valar are generally not in the habit of giving mortals this power.
Therefore are there side stories about powerful human sorcerers? and the story of how they got their powers wold be cool
Well surely they Can. Some Nazghul like Whitching of Angmar was a powerfull sorcerers. Though human sorcerers are way less powerfull then Istari.