Wikipedia has a wealth of information for learning more about fantasy in general, its history, and some commonly used tropes. I've listed several fantasy related entries below:
Fantasy - Wikipedia, the free encyclopedia
List of genres - Wikipedia, the free encyclopedia
Fantasy tropes and conventions - Wikipedia, the free encyclopedia
List of legendary creatures - Wikipedia, the free encyclopedia
Or by type: List of legendary creatures by type - Wikipedia, the free encyclopedia
Weapon - Wikipedia, the free encyclopedia
Magic in fiction - Wikipedia, the free encyclopedia
Dragons! Dragon - Wikipedia, the free encyclopedia
More writing focused stuff:
Lots of links here: Fiction writing - Wikipedia, the free encyclopedia
Plot (narrative) - Wikipedia, the free encyclopedia
Archetype - Wikipedia, the free encyclopedia
Setting (fiction) - Wikipedia, the free encyclopedia
Theme (literature) - Wikipedia, the free encyclopedia
Style (fiction) - Wikipedia, the free encyclopedia
Character (arts) - Wikipedia, the free encyclopedia
Fantasy - Wikipedia, the free encyclopedia
List of genres - Wikipedia, the free encyclopedia
Fantasy tropes and conventions - Wikipedia, the free encyclopedia
List of legendary creatures - Wikipedia, the free encyclopedia
Or by type: List of legendary creatures by type - Wikipedia, the free encyclopedia
Weapon - Wikipedia, the free encyclopedia
Magic in fiction - Wikipedia, the free encyclopedia
Dragons! Dragon - Wikipedia, the free encyclopedia
More writing focused stuff:
Lots of links here: Fiction writing - Wikipedia, the free encyclopedia
Plot (narrative) - Wikipedia, the free encyclopedia
Archetype - Wikipedia, the free encyclopedia
Setting (fiction) - Wikipedia, the free encyclopedia
Theme (literature) - Wikipedia, the free encyclopedia
Style (fiction) - Wikipedia, the free encyclopedia
Character (arts) - Wikipedia, the free encyclopedia