Every "Treatise," the base monetary unit and EXP equivalent in DnDis, is composed of ten "Pages." These Pages are automatically produced by a character when they defeat an enemy or complete a difficult action, and are also, like Treatise, units of currency.
You do not have to wait until the end of a game to spend Treatise - you can do it immediately after gaining ten Pages, if you like.
If used for experience, 1 Treatise converts to a 1 stat point or 1 skill level - at least, those are the current playtest rules. If you're interested in running a long-term game spanning several adventures, we recommend that you consider upping the cost of Skill Ranks some.