Horde refers to a large crowd or mob. It is always a noun (with rare exceptions). Hoard can be either (1) a noun referring to an accumulated store or cache, or (2) a verb meaning to accumulate a hoard. If you have a hoard of something, a horde of people might try to take it from you.
A hoard of gold coins smuggled to London by a Jewish man who fled Nazi Germany will be returned to his descendents, a coroner has ruled. [BBC News]
Players will battle hordes of zombies, cast powerful spells and must fight to keep their sanity. [Sydney Morning Herald]
He retains the largest hoard of political capital of any leader in any Australian jurisdiction. [The Australian]
Despite all this, the media horde—like a moth to the flame—congregates around the egomaniacal Donald Trump. [Washington Post]
Notably in Saudi Arabia, which hoards a glut of stored oil which is vital to stoke the world’s growing demand, spurred by emerging economies. [The Economist]