The front adjustment thingy is for your guesstimate on the yardage? 25 yards to infinity?
I get the zoom ring. The fast focus eyebell is for correcting your vision for near sighted or far sightedness? Cheap ass or not this thing has more bells and whistles than my GoldRing Leupolds.
http://www.barska.com/riflescope_manual_bc141.pdf
That is a heck of a good price.
It would be better yet in .308