A tank of around 5 gallons (20L) with a small filter, a lid, a couple of places to hide(silk or live plants and a cave of some sort), and an adjustable heater. The heater is mandatory and needed to keep a stable temperature of 78F-82F (25C-27C) to keep the betta healthy. Betta pellets and some frozen goodies(brine shrimp/bloodworms) for treats are the best for your betta's diet. There is more to it but this is a good brief overlook.