What happens when I boost?

I'd like to use one of my boosts, and I was wondering what exactly happens? I mean can I still go back to Queensdale and do all the content in order? Or does it complete all the maps and stuff as well? I'd like to complete maps and whatnot, and play through the story in order, and I know levels scale, but I'm not totally clear on the details of the boost.

You can still go back and do everything. The L80 boost does not give you map completion, personal story completion or any other progress aside from reaching L80, unlocking a few L80 wapoints, some L80 gear you get and some goodies. I added links to my post that go to relevant wiki articles.

As far as using the boost here is a tutorial video Anet put together:

Worth it tho if you have a lot of alts like I do lol

Yes you'll still be able to do everything.

The boost levels you to 80 and automatically spends all your hero points to unlock everything except the elite specialisations (which can't be trained until you've got everything else anyway). It also gives you 1 waypoint in each core level 80 map and gives you some items and gold. But that's it.

Your Personal Story will still be at whatever point it was before (but now you can do the entire thing in one go if you want since you won't have to level up between chapters) and you'll still have to do map completion the same way as before.

Oh yeah, the other difference is that any XP you gain while playing that character will now go towards training masteries, or to getting spirit shards if you've completed all the mastery tracks for that region.