After Adam (AS), we are all descended from Nuh (AS).
One day Allah revealed to Nuh (AS) that no more people would accept his message. So Nuh (AS) turned to Allah in prayer and said, ‘O my Lord, do not leave a single disbeliever on the Earth. If you leave them, they will mislead Your slaves and give birth to more wicked disbelievers.’
Allah accepted the prayer, and promised to send down a flood to destroy the disbelievers. He ordered Nuh (AS) to build a large ark. Nuh (AS) began building the ark on top of a hill outside of the city, far away from the sea.
When the disbelievers saw this, they made fun of Nuh (AS). They mockingly asked him if he wanted to be a carpenter now instead of a prophet. They also ridiculed him for building so far away from any source of water, asking him if he was planning to drag the ark all the way to the sea or if the wind was going to carry it for him.
Eventually the ark was finished. Allah instructed Nuh (AS) that when flood began, he should take the believers and two of each animal, a male and a female, to the ark. Soon water began gushing from the Earth and the sky, and Nuh (AS) hurried to fulfil Allah’s command. Even now the disbelievers mocked him, asking what he was planning to do with all of these animals. But Nuh (AS) continued to fulfil Allah’s command.
Nuh’s (AS) wife was not a believer, and so she did not join him. He also had a son who had pretended to be a believer but was really not. From the ark Nuh (AS) called out to his son, telling him to believe in Allah and join him. But the son said that he would instead climb a large mountain and be saved. Nuh (AS) tried to warn him that nothing could save him from the punishment of Allah, but as he was saying this a big wave came and swept his son away. Nuh (AS) was upset by this, but then Allah told him that his son was not from amongst his family, because he was a disbeliever.
All the water inside the Earth gushed out at the command of Allah. At the same time, rain poured and poured from the sky without stopping. The sea level rose and rose, until the water had taken over the land and for the first time the entire Earth was flooded. There was not a single piece of dry land left; even the mountains were submerged!
The survivors remained on the ark until Allah commanded that water stop gushing out from the sky and the Earth. The water level then began to decrease. Eventually, the ship landed at Mount Judi (believed to be in modern day Turkey). Nuh (AS) released the animals first, before the believers disembarked. The first thing Nuh (AS) did on dry land was to put his forehead to the ground in prostration, in thanks to Allah. After that, the survivors created a fire and had hot food for the first time since the start of the flood.
We do not know much of what happened after this. We do know that none of the believers in the ark other than Nuh (AS) had children. This was a gift from Allah to Nuh (AS). So every human from that point forward is a descendent of Nuh (AS), and we are all related to him. The final thing we know is the advice that Nuh (AS) gave to his sons when he was on his deathbed, which was to believe in no god but Allah and to never associate partners with Him, no matter what.