I won't have time to explain the uses of tithing myself, but know that the money is used in very particular ways and does not line the pockets of our leaders, though the highest leaders who do not have full-time jobs receive some modest support. It's apparent that none is exactly wealthy and that the money is not used for personal gain. Hopefully this link will help:

http://lds.org/ldsorg/v/index.jsp?locale=0&sourceId=e141f73c28d98010VgnVCM1000004d82620a____&vgnextoid=bbd508f54922d010VgnVCM1000004d82620aRCRD

(see the last two links under "Additional Online Materials" for the most straightforward information)