Your campsite contains a lovely 3-shelf bookshelf -- handsome mahogany inset with mother-of-pearl mystical runes! It's got a shelf for Tomes, a shelf for Librams, and a shelf for Grimoires...
Tomes: Tomes contain powerful spells. So powerful that you can only use your Tomes three times per day, lest you become absolutely corrupted by the absolute power.
Librams: Librams also contain powerful spells. Each time you use a Libram in a day, it'll take you more and more energy to use another one. Or the same one again. You'll get the idea once you start using them.
(Your bookshelf doesn't have any Grimoires on it.)
Notes
The bookshelf will only appear in your campground if you have used at least one Tome, Libram or Grimoire.
The bookshelf is not affected by Hardcore or Ronin restrictions. However, it is not visible while in Bad Moon, although it was once possible to access the bookshelf through direct linking. Originally it was possible to use the books normally to cast spells this way, but this was soon fixed. Trying to go to the bookshelf will just redirect the player to the campground.
Under the Zombie Slayer ascension path, the bookshelf is replaced with your open grave.
Under the Trendy ascension path, books that are not usable are marked:
Unfortunately, it's far too old to use.
Books can be placed on your bookshelf while in Bad Moon, although it is not possible to cast the spells they grant until you have broken the prism, at which point the bookshelf becomes fully available for use until you ascend into Bad Moon again.
The MP cost for summoning your nth Libram item is 1+(n*(n-1)/2), or 1+(1+2+3+...+(n-2)+(n-1)). This price resets upon rollover and ascension.
The cumulative MP cost for summoning n Libram items is (n*(n²+5)/6) or (n*(n+1)*(n+2)/6)-(n*(n-1)/2).
The bookshelf was implemented on January 3rd, 2008, as a way to limit the disadvantage that new players down the line would experience by missing out on powerful, limited-time-only spellbooks such as the Tome of Snowcone Summoning. Prior to its implementation, spellbooks granted their skills, automatically marked Hardcore Permanent, directly to players.
Outside of Hardcore/Ronin, you can use each Tome you own three times per day. Inside Hardcore/Ronin, you can use your Tomes three times per day total.
References
The description of the Tome shelf references Lord Acton's famous dictum: "Power tends to corrupt, and absolute power corrupts absolutely."