The bracket is a piece of specially shaped metal or ceramic that we affix to each tooth. The wire threads through the brackets and, as the wire tries to return to its original shape, it applies pressure to actually move your teeth. Picture your tooth resting in your jaw bone. With pressure on one side from the archwire, the bone on the other side gives way. The tooth moves.
New bone grows in behind.
Thanks to new materials and procedures, all this happens much quicker than ever before. It's kind of an engineering feat. Rubber bands or elastics contribute a lot to straighter teeth. They are marvels of physics. Attached to your braces, elastics exert the energy force that creates the right amount of pressure to move teeth.