What are "bonus spells"?

[joonkimdmd]

Wisdom, intel, charisma description says
This and this class gets bonus spells based on these stats.

I just changed intel modifier 6 into 9 for wizards, but the number of spell slots in spellbook stays the same from level 1 spell all the way up to level 7 spells.
So it doesn't change the number of spell slots which is equal to the number of spells I can cast.
So what does intelligent do for wizard class?
What's the bonus spell it is refering to?

And is bonus spell different from # of bonus spells?
Intel and Wisdom says "bonus spell" but Charisma says "number of bonus spells" increase.

[Finrod]

Casting attribute 18
One bonus spell Slot, at level 1 to 4

Attribute at 20:
2 bonus spells slots at level 1 and 1 from level 2 to 5

Attribute at 22
2 bonus spells at level 1 and 2 and 1 bonus slot from level 3 to 6
Etc

If it does not happen it is a bug

https://www.d20pfsrd.com/basics-ability-scores/ability-scores/ (table abilities and spellcasters)