In the beginning there was nothing, an infinite dark swirl in a watery chaos called Nu. Out of this chaos rose Atum who created himself out of his own will and thoughts.
Seeing as everything was watery and in a state of chaos, Atum created a Hill for him to stand on with the rising of the sun god Khepri. Now, Atum was all alone in the world, so he made a mate with his shadow (Atum was widely believed to be both male and female).
He had two offspring, he spat out his son Shu, god of the air, and vomitted out his daughter Tefnut, goddess of moisture. Shu condoned the ‘principles of life’, while Tefnut oversaw the ‘principles of order’.
Soon, Shu and Tefnut became separated from their Atum, and with his one over-seeing eye (known as the Udjat eye), he found them. He wept with joy during their reunion, and from his tears man was created from the earth.
From there, Atum created the rest of the world, so Shu and Tefnut became the parents of the earth god, Geb, and the sky god, Nut. In turn they created Osiris, Isis, Seth and Nepthys.
PS: There are a few creation myths in the Egyptian culture, like any other ancient culture, so this is only one of them.