Brown flour is a lot more absorbent - so you'll need more liquid - and a lot tougher, so if you're planning to knead or roll anything you'll have to put more muscle into it. It's usually okay, though; if you have doubts, sifting it will usually get out a lot of the bigger bran. Much better for you, in any case.

Molasses is treacle - sugar halfway through the production process. Way back when you couldn't buy sugar powdered - it either came as molasses or as a huge, rock-hard block which you had to chisel lumps off.