A book might contain poetry, historical accounts, information pertaining to a particular field of lore, diagrams and notes on gnomish contraptions, or just about anything else that can be represented using text or pictures. A book of spells is a spellbook (described later in this section).
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.