I think the key thing you ar missing is on p. 14: "...for each experience point a wizard gets, he gets 1 point for learning spells." Those spell learning points based on experience are applied directly to learning spells based on the table at the top of p. 15.
Let me give you an example. Let's say that you have an elf wizard with 20 intelligence and 20,000 experience points (level 4). You have two important derived characteristics here, spell learning points (used to gain new spells) and spell points (used to cast the spells you know).
Spell Learning Points = 2000 (elf) + 2000 (starting wizard) + 20000 (wizard experience) = 24000
Spell Points = 2 (elf) + 5 (INT - 15 as a starting wizard, see text on p. 14) + 8 (2 per level from level 1 through 4, see table on p. 14) = 15
So far, you can cast a lot (15) of nothing, because you haven't spent your spell learning points yet. Let's buy one of those. Let's say you wanted to focus on buffing your party, so you want to buy Speed II (level 4, p. 36; note that there is no level restriction on spell learning provided that you have enough spell learning points). Learning Speed II at 10% chance of failure will cost you 8000 spell learning points (table, p. 15). You might want to add another "big" spell for offense, say Fire III (level 3, p. 32). If you go for 10% failure on that, it'll cost you another 4000 spell learning points. At this point, your spell learning points are half gone, but you've bought two nice "go to" spells at a reasonable chance of failure. If you decided you weren't happy with the risk of frying your party in battle, you might spend an additional 1600 spell learning points (5600 - 4000, see table on p. 15) to get the spell failure on your Fire III spell down to 5%.
Based on the last table on p. 14, each of the spells you just bought costs 1 spell point to cast. So you could cast those 2 spells in any combination up to 15 times a day, possibly more if you had time to rest (see Recovery, p. 54).
I hope that helps.
