RollQuest summary of the SRD 5.1 rules, not a quotation.
Choose a type of favored enemy: aberrations, beasts, celestials, constructs, dragons, elementals, fey, fiends, giants, monstrosities, oozes, plants, or undead (or two races of humanoid). You have advantage on Wisdom (Survival) checks to track your favored enemies and on Intelligence checks to recall information about them, and you learn one language they speak (if any). You choose one additional favored enemy, and an associated language, at 6th and 14th level.
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.