Star Wars fans come in two types: fans of just the movies and fans of the entire franchise (including the books, comics, tv shows and games).
Ever since the Mouse House bought LucasFilm and declared the old expanded universe as "legends" and no longer official canon, they have slowly been constructing a new expanded universe. Every comic, book, tv show and game that is now being released is official canon.
Lots of these books and comics take place in time periods between movies, so those fine people over at Collider Video on Youtube have cobbled together all the available information to explain what happened to Luke from the end of Return of the Jedi to his appearance in The Force Awakens.