On a "regular sink" the edge will be 'flat'.. so that it lays on the counter top...(there will be a slight bow in the flange, to recieve silicone caulking for that water tight bond).
On an under the counter type, there will be a machined recess. hmm how to explain this? it will basically be an inverted U so that the fasteners will go into the top of the 'U' and the edges of the 'U' will hold them securely from moving.
Generally, a drop in, is easy for a homeowner to mount, but, putting that one from the bottom? I always liked to turn the entire countertop on its top, so that I can work staring down at the thing, and get the fasteners secured to the bottom of the counter. 2 per corner, and one in each middle...Simply because 'thats' the only thing holding that from falling off LOL
I wish you well...
Jesse