Hit points in this game are a stat. They can be increased like any other stat (see stats for rate of increase). New PCs start with one hit point (level 1). If you intend to play a character that never engages in combat, you won't have a lot of need to spend points improving your HP. However, if you do expect to engage in combat, even by chance, it's a good idea to spend some points on hit points.
HP healing
Damage is healed by time. In order to heal at all, a character is required to eat food appropriate to the diet of their species until healed (any character can eat any food normally). For regular healing, eat the appropriate food. For medium healing, a bandage can be applied by anyone, skill or not. For faster healing, a character with the appropriate skills can apply a bandage. The higher the healer's relevant skills, the faster the wounds heal. This is not rolled but is calculated from the raw stats/skills.
HP point stat equals HP available