How do you take dragonfly what does it eat?

I am not sure what "taking a dragonfly" is, but I presume you mean "catching" one. If they are flying, use a butterfly net. If that is too hard, than look by the water for ones that have fallen in. The will be probably near death, so be gentle, and use a net or a jar with holes to capture them. Also, dragonflies usually eat smaller insects, such as gnats and mosquitos. Hope this helps!