Hit Points:
For first level characters, add the maximum of the die indicated below. So a monk will get 8 HP at first level.
For every level after the first, roll the die listed for your class below. In the case of our monk, he has 8 HP for first level, and rolls a 3 on his second level die, giving him a total of 11 HP
Barbarian - roll d12.
Bard - roll d6.
Cleric - roll d8.
Druid - roll d8.
Fighter - roll d10.
Monk - roll d8.
Paladin - roll d10.
Ranger - roll d10.
Rogue - roll d6.
Sorcerer - roll d4.
Wizard - roll d4.
Add constitution bonus, if applicable, from you ability score modifier in section F. These are the initial hit point rolls for each class. So if our monk from above has a constitution of 14, we can see that this gives him an ability score modifier of +2. This Constitution bonus gets added into the hit point level at each level. So at second level, our monk has:
8 HP (maximum for 1st level)
2 HP (CON bonus for 1st level)
3 HP (die roll for 2nd level)
2 HP (CON bonus for 2nd level)
15 HP Total
If you are not sure if you have a Constitution bonus, go here.
Multi-classed characters gains hit dice from each class, with the resulting hit points added together.
See the Prestige classes for individual hit points.