Lets say i want to host my own instance of lemmy i will buy some domain and hosting server i will run an lemmy instance and then i can just start adding other instancies and post something on them or they also meeds to approve my instance?
Yes, once you have a server and domain you can read the lemmy docs and set up an instance of your on that server at that domain. You can then make an account on your own instance, and from that account do all your subscribing and posting and commenting on all other instances which haven’t defederated from your instance, which at the start will be none, and will probably remain so unless you start doing something unsavory. You can open your instance up for others to register or not. Regardless all communities created on your instance will also be available to every other instance (again, barring defederation).
selfhosted should have more helpful answers
Most of the servers running lemmy have federation enabled and open (as you can see, I’m one of those self-hosted instances) and you can just interact with them. Some do have federation locked down, but that’s the minority
Do you need a domain for a selfhosted instance? That sounds like something I would like to try but I’ve never opened anything selfhosted up to the internet
Yeah you do, IPs don’t work afaik and even if they did, many Fediverse servers don’t support them so your compatibility would be abysmal
