Welcome! The 15-day "honbasho" tourneys are every 2 months, and next one starts the 2nd Sunday in November! (there are also exhibition tourneys in-between but I don't follow them... I think they're having one in London soon?!?)
If you want a quick intro see the following:
If you want to catch up on the recent tourney, see one of these (will be taken down soon):
- https://www3.nhk.or.jp/nhkworld/en/tv/sumo/
- https://www.youtube.com/playlist?list=PLFEzXnIQVwV9JgQkOMJZM23G8g-wBBWKf
HAKKEYOI!!!