All it is, is a battle with Lv. 1 Pokemon that has no EVs at all. The battle has to be at lv. 100 to check out the stats at the maximum level. You just write them down and put them in the IV calculator and it will give you the exact IVs it has.
For instance I have 10 Zubats I have to check, I want to get the 31 spe IVs. When I'm done I'm just going to runaway.