1) Offset is the amount of gap between the leading edge of the clubface and the frontmost part of the hosel. Typically, game improvement clubs have more offset as it gives the clubface a split-second more of time to try to square up to the ball. Since most novices slice the ball, this is supposed to help their problem
2) Forgivness is the amount of distance that is lost on a shot that isn't struck directly in the centre of the clubface (i.e. hit more towards the heel or toe of the clubface). A club with a lot of forgiveness would not have huge variances in distance between a shot that was pured and one that wasn't.
3) Getting better clubs will not necessarily yield more distance. Factors that determine difference are whether the clubs are properly fitted to your swing (shaft, lie angle, etc) and loft angles of the two sets of irons. I'm sure there are also other factors that affect distance.
I would suggest for whatever set of clubs you decide to buy, you should definitely definitely get fitted before you buy them.
It'd be good to know what handicap you play to, but a decent set of irons I've played with are the Taylormade LT's (not the LT2s). They have a bit of offset, had some forgiveness, felt nice and soft when struck well and were aesthetically appealling (to me at least). Also, since they're a couple years old now, you can probably pick up a set for a decent price.
Hope that helped and best of luck on your club search!
