[quote=@CajunRobinHood]
So, in layman's terms, how are we doing HP?
[/quote]

I don't want to step on [@Game Maker] toes but usual way to do HP is like this.
A fighter has 1d10 for their hit dice, at first level you take the max roll plus your constitution modifier. Then for each level after that you roll your hit dice and add that number to your HP plus your consitution modifier again. So lets say I rolled a 4 for level 2 and a 6 for level 3 and my constitution was 14 so I had a +2 modifier.

Level 1: 10+2=12
Level 2: 12+2+4=18
Level 3: 18+2+6=26

Each class has a different hit dice too
Barbarian 1d12
Bard 1d8
Cleric 1d8
Druid 1d8
Fighter 1d10
Monk 1d8
Paladin 1d10
Ranger 1d10
Rogue 1d8
Sorcerer 1d6
Warlock 1d8
Wizard 1d6