The benchmark runs a short in-game scene then reports back with your average and maximum frames per second scores--not the most in-depth analysis but certainly enough to give a fair indication of how it'll run and to compare excitedly with your chums.
Bizarrely, you'll need to log into a uPlay account and have the uPlay launcher open to run the benchmark. H.A.W.X. 2 will indeed be using Ubisoft's wacky DRM scheme.
While H.A.W.X. 2 was release on Xbox 360 and PlayStation 3 in September, the PC version was delayed and is now due some time this month.