How did the first flying insects look like and when did they first appear?

Answer 1

The earliest fossils of winged insects have been found in Scotland and date to the Early Carboniferous Period of about 350 million years ago. They were dragonflies. Modern forms still resemble their ancient ancestors.

Answer 2

They were huge because of the amount of oxygen, allowing their respiratory systems to be smaller, and the meganeura monyi had a 2 foot wingspan looking something like a dragonfly.