How a floodplain forms and why do people live on flood plains?

It is formed by erosion, they live their because there is alot of space there really

Floodplains are either formed by erosion or by aggradation.

People might want to live here, because the sediments in the river make the soil rich, which is good for farming. There is also plenty of water around because of the rivers, and the rivers can be a form of transportation. The river can also be a food source.