Hummingbirds are not very romantic. The male hummingbird will go through some great lengths to impress a female, doing exhausting dances and aerial maneuvers to show how strong and wonderful he is. If a female is impressed enough with his genetic material as proven by his fitness, she will allow him to mate with her.
The actual mating will last only seconds. They press their cloacas together in what is known as a "cloacal kiss" and sperm is transferred from the male to the female. As soon as this is done, the male will leave and go off to try to impress another female.
The female hummingbird will build her nest, lay two eggs and raise her chicks by herself. In fact, she will even protect the nest and her chicks from the male who inseminated her.
In some hummingbird species the males will congregate in "leks" and all sing together to attract females to the area. The dominant male is usually in the center. The less dominant males are relegated to the edges of the lek. This method works better in many areas of South America where there is not enough wide open space for the males to perform the big aerobatic pendulum maneuvers of the more northern species. When a female approaches a male, he will dance for her, flash her his gorget and the courtship continues.
This video was taken of a male Anna's hummingbird displaying to a female. She is impressed enough to allow him to mate with her. Afterwards she hangs upside down on the branch for a full minute. You can see her tail pulsating as she hangs there. She then pops back up. The male has already disappeared to find the next female who he can impress. (Background noise is a television that was on.)