thats a good question and people ask me this a lot.
all you do is order the test you want, pay with a credit card, print the orders out. and take it to labcorp. when you get there when its your turn they take you back and take the paper from you. ask you your date of birth (to make sure they got the right person) and they will sometimes ask if you have been fasting (just say yes who gives a fuck, reason they ask is cause a hormone panel includes glucose and it won't be accurate unless you fast but who gives a fuck about glucose we care about the other shit... if you care about glucose then fast all night) then they draw your blood and then you leave.
a few days later you go online and like magic your results are downloadable.
sometimes they also will say "oh you were supposed to get tested before 8am and now its 8:30".. since testosterone is highest upon waking they will say this.. i always just tell them "my doc wants to see where my numbers are after 8am" i mean really who gives a fuck if i get tested at 8am or 8:30? like its gonna make THAT much of a difference.. i sometimes want to tell them "mind your own fucking business and just draw my blood" lolol