Egg production

Most birds have only one ovary and one oviduct. In early stages of embryonic development, each female bird has two ovaries; only the left one develops into a functional organ. In some birds, such as peregrine falcons, the right ovary and oviduct usually develop. A mature ovary looks like a cluster of grapes. and may contain up to 4,000 small ova which can develop into mature ova.
With fertilization, the ovum or egg becomes a developing embryo
The embryo passes through the oviduct typically takes about 24 hours (for passerines & most other birds)
The demand for calcium to make the egg shell is very high, and so the circulating levels of blood calcium in birds are greatly elevated compared to mammals, typically twice as much.

The ovary enlarges greatly during the breeding season. Active ovaries resemble bunches of tiny grapes -- the developing follicles. The oviduct opens medially to it in a funnel-shaped ostium. Ovulation results in the release of an egg from a mature follicle on the surface of the ovary. The egg, with extensive food reserves in the form of concentric layers of yolk, is picked up by the ostium an ciliary currents carry it into the magnum region. Over about three hours the egg receives a coating of albumen. The egg then passes into the isthmus, where the shell membranes are deposited. This takes about one hour. The egg them moves to the uterus, or shell gland, where the calcareous shell is added and, in some birds, pigment is added in characteristic patterns. The egg then passes into the vagina and cloaca for laying.