On the first page of your class, where it has the iconic art, class skills, etc., it says "X HP" in the upper right corner. You gain this many HP each level, whereas the HP from your race are only added when you're making your character at level 1. Just left of the HP, it says "Stamina Points: Y + Constitution modifier". Every level, you gain that many Stamina Points.
The space goblins have been pulling wires in the server room almost every day for the last month.