As "ClipperDelta" already stated ... Congratulations on your achievment! What you will receive is a Hartman luggage tag and a Hartman ticket jacket. Not like the old days (make that when Delta made money) when MM status was attained by adding all mileage earned (1000 mile minimum, 100% and even triple miles bonuses in the late 80's as well as miles earned at car rentals and hotels, usually 1000 miles as well). They actually gave away a real peice of Hartman luggage (though it started with a notebook I think and other very nice amenities. It now takes anywhere from 5 to 8 times as much actual flying to attain MM status today! There are some other airlines I believe that recognize this milestone (American for one) but most do not so whatever Delta gives you be grateful for as my dear mother used to say "Its still better than a sharp stick in the eye" , Mom .... always the optimist!
As for not understanding the pecking order for upgrades ... don't feel bad as even the folks on this formum who claim to "know" sometimes are stumped when they are standing by at the gate and partcipating in the "lottery".