The text sometimes calls them the longer “psi power points”, which searching on will find you the right section. How many a character gets is detailed at the end of the Character Creation chapter in the “Final Touches“ section, under “Psionic Powers” (on page 23 of the Core Edition).
Effectively, a Psychic gets 1 + the higher of their Wis or Con mod at 1st level, then at each level up that cap increases by the better of their Wis or Con mod plus the amount in the Psychic class's XP table (Core Edition p. 19) for that level.
Charity is a 1st-level Psychic. She has a Wisdom of 12 (mod: +0) and a Constitution of 16 (mod: +1). To calculate her psi points she starts with 1 and adds the better of her Wis and Con mods, which is the +1 from Con. She has a total of 2 psi points at 1st level.
When Charity reaches 2nd level she consults the Psychic XP table and sees that she gets +3 psi points + the better of her Wis or Con modifier (again that turns out to be the +1 from Con) for a total of +4 psi points gained. Adding that to her existing psi points, she has 2 + 4 = 6 total psi points as a 2nd level Psychic.
Aside, non-psychics gain no psi points at 1st or later levels, not even just a base from their ability mods. (That's assuming that the option in the GM's section to have everyone be a little bit psychic isn't being used, of course.)
Mercy is a 1st level Warrior. She has Wisdom 14 (mod: +1) and Constitution 15 (mod: +1). Because she is not a Psychic she gets zero psi points and no bonus psi points from her Wis or Con modifiers. Mercy has zero total psi points as a 1st level Warrior.