How do they fly?

Very carefully.

Seriously, the answer to your question can be found at the following link. Good flying:
https://askabiologist.asu.edu/how-do-birds-fly

A birds' feathers are shaped so that air travels faster over the top of the feathers than do the bottom. This creates a sort of vacuum over the feather giving it lift. This is how a bird can stay "afloat" in the air, by moving air over the wings. This is also how a plane is able to fly.

Birds have many physical features, besides wings, that work together to enable them to fly. They need lightweight, streamlined, rigid structure for flight.