Can you be more clear? Are you just trying to find a mob on a specific spot? For instance if we wanted to detect a zombie at 200 68 1200 we would do.
Then if you want to do it the fancy way. Which is actually not that fancy, it's the way that Java did it and it's actually why Java remove the testfor command all together. Say you wanted to test for an entity then setblock redstone somewhere, instead of doing a