This is the most basic way to set up for de-ashi-barai. It's not the most realistic way to do a footsweep because people don't normally move this way but it's the way the fundamentals of footsweeps are taught.
To learn more about de-ashi-barai and other ashiwaza, check out this video from Judo Fanatics: https://judofanatics.com/collections/all/products/demystifying-ashi-waza-by-shintaro-higashi
