“Hoard” (as a noun) is a large collection of something. It is usually something of value, such as money or food, and is usually either hidden in a secret place or carefully guarded. “Hoard” (as a verb) is the act of creating a hoard.
“Horde” is also a large collection, but it is a collection of people or animals, usually with the inference that they are swarming and about to attack…a horde of mosquitoes came through the back yard, a horde of nomads suddenly appeared out of the desert.
Keep them separate by remembering that “Horde” and “people” both have an “e”, while “hoard” and “valuables” both have an “a”. During the potato famine, I’m certain that a horde of Irishmen hoarded potatoes.