Again sorry for the noob question but Iread the rules a couple of times and there is no example in the book.  Would a level 2 wizard (D6 die type) with a Con Bonus of +1 roll 2d6 +2 (con bonus per die) [e.g. I rolled 2d6 for a 7 +2 = 9hp] and then add that number to their existing hit points (7 +9 = 16 HP).. At 3rd level one would roll 3d6 +3 (I rolled a 12+3 =15, 15 Plus 16 = 31 HP. Is this right? At this rate the players will have a lot of HP. I think I'm reading the rule wrong or something. 

A 1st level Wizard with a Con mod of +1 gets 6+1= 7 HP at 1st level. When they hit level 2, they get an additional 1d6+1, at level 3, they get another 1d6+1, and so on. If they ever raise their Constitution score to the point where their Con mod becomes a +2, then all of those +1 bonuses become +2 bonuses. That change does get applied retroactively.

Thanks ,that makes a lot more sense.

Happy to help

Hold on... an increase in constitution modifier increases hit points retroactively? So my fighter gaining +1 constitution modifier at level 8th level gains 1d10 + CON mod + 7 hit points?

Yes. If you use the DDB character sheet it should automatically calculate that for you.

Well, blow me down. I'm glad you asked, Leif!

you are welcome.