If you pay the $0.99, you will get:
- 5 more moves
- 3 Lollipop boosts
You can still lose, even with 5 more moves. If you do, you'll be back on this screen again. Thus, if you don't think you can win with just 5 moves, this is probably a terrible deal. (Although I think it is a terrible deal all the time, but that's me)
The lollipop boosts can be used anytime, and they will break a candy in a single square, with all the effects that entails - so they will clear jelly underneath the candy, for instance.
Paying for this has no effect on your lives - paying for extra lives is a different thing altogether.