in No Limit bb = big blind. so in 1/2 NL (which i dont recomend you try starting at if you are really just starting out, unless you have lotsa cash that you can afford to lose) it would be 2 dollars.

Normally 1/2 - 2/3rds of the pot as a "continuation bet" is a good amount if your opponent completely missed. Thats not really a hard and fast rule, it will differ from opponent to opponent, but thats pretty standard continuation bet size. So in your case, 3-4 dollars.