When you reach 39 you will get a prompt to visit your class trainer where you can buy three books! You will then have to gather the pages to fills those books by killing mobs.
It is important to talk to the NPC mentioned in the relevant quest before commencing to find the pages. The pages do not begin to drop until you talk to the relevant NPC to progress this initial part of the deed quest.
There is some debate that the old class deeds for the pages of the legendary books are now passe, but I beg to differ! I think they are integral to your build! The legendary books now unlock a trait point each. Which is helpful. But now there is no rush to do that! Wait until you are in Moria and the pages will drop when you kill humanoid mobs. Although as you play and quest you are bond to collect some pages.
The mechanic of page collection is kinda rough. The RNG rolls for a page. That page that "drops" might be one you already have. If that is the case, you won't even be notified that the page dropped at all. So the player's experience is going to be that the first few pages drop slowly. After that, the next few take quite a while. When you are trying to get your last few pages in a region, it can feel like they will never come at all. Fortunately! Moria drops all 8 pages and at a higher rate than the other regions.
Remember that getting the points is still important...if the OP does not do these, he will be missing 3 class points.
Good luck with your books!