Dry hopping is the addition of hops, after fermentation has finished(usually day about day 4 - 7 of the process). this could include hops in the keg too I guess. Dry hopping adds mostly aroma with a little bit of flavour. Doing the Boil option adds more flavour, and some bitterness, and little aroma. To keep it simple do the 5 - 10 minute boil option first. Next time I would do the boil and dry hop to get both flavour and aroma. As TheBig D has pointed out, dry hopping only with a little amount of hops gives aroma initially but the intensity dies off quiet early.
Once you get further into hops additions you will add hops to a boil at varying stages to get different results. the longer the boil the more bitterness is imparted, and the less flavour and aroma. typical kit and kilo additions in a boil, are 20 minutes, 10 minutes 5 minutes 0 minutes and dry hopping. 0 minutes means you add hops once you've stopped the boil and are cooling the wort down. In reality, you can add hops at any time to get the desired result, from 0 to 60 minutes!