EMS is ethyl-methanesulfonate. It's a compound used to cause random point mutations in organisms. Basically the idea is to treat a whole bunch of plants with the compound and try to cause mutations that might exhibit a trait of interest, like disease resistance or increase crop yield.

What you'd do in this case is take a tuber and dunk the meristematic tissue (i.e the little eyes on the tuber) in a solution of EMS to induce mutation and then grow all the little eyelets on some sort of growth media, usually MS agar or something similar. EMS and the growth media can be ordered online. In the lab you'd typically have access to things like a laminar flow and autoclave, but you can use a plastic box and pressure cooker instead. It's a bit dodgy, and you might get some plate contamination, but if you're careful it shouldn't be unmanageable.