The player's handbook describes the process for determining ability scores via 4d6 drop the lowest (or, actually now that I think about it, it might just be 3d6 and the 4d6 drop might be another variant rule). But I have very rarely actually used that, and instead used the 'point buy' system, starting from 8 and 'buying' points up to a maximum of 18.
I can't find a source for that in the PHB, the DMG or the SRD. Where did it come from? A 3.0 book? A 2e book?
Best Answer
Point buy is described in the DMG
In Dungeons and Dragons, Third Edition, the Dungeon Master's Guide on page 19 on Ability Scores Generation describes Standard Point Buy.
In Dungeons and Dragons 3.5, the Dungeon Master's Guide on page 169 on Ability Scores describes Standard Point Buy.
The SRD deliberately omits the process of creating (and advancing) a character so that folks must buy Player's Handbooks (and maybe Dungeon Master's Guides and Monster Manuals) to play d20 System games.