Newbie Quickstart Guide

If you're totally new to sumo and want to know where to start, here are the basics to get you up and running. There many other options than the ones I listed below, but these are the most convenient, best quality and newbie friendly options to easily get you going.

OK, so how can I watch sumo?

To watch live:
Overall I recommend MidnightSumo (https://www.youtube.com/@MidnightSumo/), which has Japanese commentary. The chat can be a little "lively" sometimes so just hide it if it bothers you, but they're very friendly and willing to help out if you say you're new. His stream shows all divisons, but the top division starts at about 4pm Japan time.
If you want the English commentary, check out So Desu Ne (formerly called MbovoSumo); NHK are extremely proactive in removing the English commentary it seems, so his stream often gets taken down. Right now you can find it on Kick (https://kick.com/dondondondon).

To watch highlights:
Obviously NattoSumo is the best way to watch highlights.... but NHK have been chasing him all over the internet and he's basically been banned from every video website by now. Right now his Ugetube seems to be the only stable place he can upload (https://ugetube.com/@sumochanko), but something is in the works and will be ready soon that will last a bit longer hopefully. Check the "Match video and streams" page for links to all his other sites.
If Natto is down, Kintamayama is the OG of this thing and you should check him out. https://rumble.com/user/Kintamayama 

• I don't understand anything! How can I learn more about sumo? 

NHK World's Grand Sumo Highlights website (https://www3.nhk.or.jp/nhkworld/en/tv/sumo/) has a lot of great resources for beginners. The links at the top have a lot of info: the "Sumopedia" series of videos is great at explaining some of the concepts, rules and history of sumo. The "Techniques" page has videos on every single winning technique, or "kimarite" in sumo; you don't have to watch them all but it's great at breaking down the many ways to win. There's also the "Basics" and "Q&A" pages to fill in any gaps in your knowledge. It even has an official highlights show of all the top division matches, but the website is a day behind sadly so NattoSumo is your best bet for saying up to date.
If there's something you're still unsure about, feel free to ask a question in the NattoSumo Discord (https://discord.gg/nattosumo); there's a room called '#sumo-q-and-a' which is specifically for asking questions about sumo, no matter how simple or complex.

• OK, I understand the basics now, where can I get more involved?

This very website has a ton of different sumo resources to learn more and get your sumo fix. I recommend joining some Discord servers for chatting; the afforementioned NattoSumo Discord (https://discord.gg/nattosumo) and Grand Sumo Discord (https://discord.gg/Wg4DsMt) are the biggest sumo Discord servers.
If you like forums, Sumo Forum (http://www.sumoforum.net/forums) has been running for decades and is full of extremely knowledgeable people.
I would also highly recommend Sumo Reference, commonly known as SumoDB (http://sumodb.sumogames.de/), a statistics website with results going back 300 years! It's a little unreliable and old-looking, but if you like your stats there's literally nowhere better; it's even better than the official website!
If you want to take things further, there are plenty of sumo podcasts to listen to, Youtube channels to watch, news sites to read... you can find all of these on the relevant pages of this very website, navigation at the top!