DMI represents how well a player is going to play in the upcoming game. But never go strictly off of it as it's really just a rough estimation. NEVER use it as a tool when buying players as it goes up and down radically with Game Shape.
TSP - Total skill points. Just adds up the number of skill points a player has.
When buying players, skill location is more important than TSP. For instance, if you need a PG, a PG with only 90 TSP, 20 OD, and 15 PA is going to be better than a 100 TSP with 15 OD and 11 PA player.