You might think that fantasy novels are limited to "The Lord of the Rings" and "Game of Thrones", but there is actually a lot more to this genre. It's defined by magic, supernatural powers, imaginary creatures, and the paranormal. They can be set in entirely fictional universes, or they can be set in our own real world with the addition of these magical elements. The plots usually revolve around battling empires, battling families, good vs. evil, etc. Some of it can be similar to "soft" science fiction, but what differentiates fantasy is that it is always based on magic, not on anything that is scientifically possible or could at some point become scientifically possible.
High fantasy (or "epic fantasy") is characterized by plot and themes of epic scale- sometimes, so epic that an entire series is needed to cover the story arc. High fantasy novels are always set in their own universe separate from ours, with its own rules and physical laws. Traditionally they were set in civilizations reminiscent of western Europe in the Middle Ages, but they are increasingly more diverse and of course can be set in any culture or time period. They can just as easily feature spaceships and aliens as dragons and castles. Try these authors: J.R.R. Tolkien, George R.R. Martin, N.K. Jemisin, Terry Pratchett, Terry Brooks, Terry Goodkind, Guy Gavriel Kay, Patrick Rothfuss, Brandon Sanderson, Mercedes Lackey, Joe Abercrombie, S.A. Chakraborty, Nnedi Okorafor, Naomi Novik, J.K. Rowling, Neil Gaiman, Tomi Adeyemi
Low fantasy novels are set in our own real world (in any time period), but with magical and supernatural elements. If the characters are not surprised by these magical elements and act as if they are normal, then they can be further subdivided into the "magical realism" genre. Try these authors: Gabriel García Márquez, Jim Butcher, Silvia Moreno-García, Alix E. Harrow, Carlos Ruiz Zafón, Salman Rushdie, Haruki Murakami, Alice Hoffman, Sarah Addison Allen, Neil Gaiman, Emily Croy Barker, Erin Morgenstern
Paranormal romance is a very popular subgenre and is any romance that features supernatural elements. This is the group where all the vampire, shape-shifter, werewolf, fairy, demon, etc. romances go. Some popular authors in this subgenre are Charlaine Harris, Christine Feehan, Gena Showalter, Nalini Singh, Karen Marie Moning, Sherrilyn Kenyon, Kresley Cole, Patricia Briggs, Laurell K. Hamilton, and Deborah Harkness
Think Aesop's Fables, Arabian Nights, and Grimm's fairy tales. These are some of the earliest examples of the fantasy genre, and show the length of the genre's literary history.