There's a driver you have to install which creates the virtual monitor in Windows, and sends 60 pictures a second to a chip that's at the end of the usb cable.
The chip takes the pictures and creates the VGA signal.
So in effect you have a "video card" but it's minimal and uses a lot of cpu to send the images to the usb chip and has practically no support for games and anything advanced. Even video playback at 1920x1080 may be choppy if you have a weak cpu.
For office work and stuff like that it works.
You'd be better off buying some cheap video card off eBay ... for example here's a lot of 6 AMD HD6350 video cards for 20$ plus shipping, so around 4$ each : https://www.ebay.com/itm/Lot-of-6-AMD-Radeon-HD-6350-ATI-102-C09003-B-Video-Graphics-Card-512MB/163541970560?epid=708334208&hash=item2613dc6e80:g:opsAAOSwYNdcZIzq
Add a 1-2$ DMS-59 to 2xVGA / 2xDVI adapter cable and you're set with a video card that at least has hardware decoding, can play youtube videos and drive 2 monitors.