Erect means "build" or "upright." If you erect a house, you build it. If you stand erect, you hold your body as tall as possible.
Erect comes from the Latin word erectus, meaning “upright, elevated, lofty” or “eager, alert, aroused.” Erect is a verb, as in, it will take you years to erect your replica of the Eiffel Tower using only gum and toothpicks. Erect is also an adjective, as in something that is tall, firm, straight or rigid, like a half-dead plant that becomes more erect when you water it.