How is drag created from wingtip vortices?
Wingtip vortices don't create drag, just as wet streets don't cause rain.

Lift creation and viscosity create drag. Drag is composed of pressure drag and viscous drag, and induced drag is one part of pressure drag. Unfortunately, the Internet is full of memes which attribute induced drag to those wingtip vortices, but some swirling air behind a wing can hardly cause any drag, can it?

See it another way: If the wing were not creating any lift, the air would not flow around the tip and curl up. So why don't we read that the tip vortex is the source of lift? This uses the exact same logic as saying that the tip vortex creates drag, and is equally wrong.

Wingtip vortices are just the tip of a full vortex sheet which leaves the wing. This vortex sheet is the consequence of the wing accelerating air downwards. Now instead of repeating myself all over again, please allow me to point you to the many other answers which explain what is going on:


This answer explains in detail how lift is created and how the downward acceleration of air is accomplished.
This answer goes into the formation of the wake and the wingtip vortices.
This answer shows why more wingspan reduces induced drag. It matters little whether the wingtips are turned up, down or continue straight: A larger wingspan reduces induced drag.


Winglets increase the amount of air involved in lift creation and reduce induced drag for the same lift. In most cases they are used to create more lift with the same geometric wingspan without incurring a disproportionate drag penalty.