Dust is simple, just go to craft in 'my collection' and x amount of dust is required for certain cards. On the bottom right you can always disenchant extra (it will only d.e duplicate cards). Mostly every type of class has a deck name i.e casino mage (more luck base cards involved)/tempo mage freeze mage .etc.

Theres a bunch of hidden quests that you probably wouldn't know about starting off

http://hearthstone.gamepedia.com/Quest scroll down half way-ish

I'd definitely start buying general packs first. The game will change pretty drastically when the new expansion hits... definitely play standard mode when it comes out (more beneficial/better for new players)