As others have said … it’s basically up to you … subscribe to any or all!
To provide some broader perspective … it can be a confusing part of the space here, especially if you’re coming from reddit where all sub reddits have to have a distinct name.
In effect, there isn’t that much of a difference between here and reddit. Sub-reddits with (slightly) different names were often about exactly the same thing but with different moderators and cultures or vibes. That’s basically what’s going on here when multiple communities have the same or very similar name. They’re not the same thing, they just different communities focused on the same topic, with different moderators and (sometimes at least) different cultures, moderation policies and vibes.
Some things which are different here:
Lemmy is decentralised, meaning that it’s made of multiple servers that share their data with each other but are all essentially independent.
This allows the users on completely separate servers to interact as though they’re on one server (like on Reddit). But, when two communities are on two different servers (often called instances), they can be more independent from each other than on reddit.
This manifests largely in the ability all servers have of deciding which other servers they do and do not share data with. Not sharing data is often referred to as defederation. When a server defederates from a another server, users of that defederated server can no longer interact with a community on the server that’s defederated them.
Because of this, any two communities, while focused on the same topic, may have not just different cultures but different groups of people/users that are physically able to interact and post there.
A famous example actually of this is actually that lemmy.world and beehaw.org are defederated from each other (actually beehaw defederated from lemmy.world). This means that users on those two servers are not interacting with the technology communities on the other server. Users on lemmy.ml, however, like myself, aren’t defederated from either, and so I am and often do interact with all three technology communities. Given your server, you’re probably in the same boat.
Generally, people not accustomed to this complexity find it either confusing or even unnecessary. My take is that it’s a different kind of friction that is the trade off for more independence, freedom and robustness, as lemmy is now made of over a thousand independent servers, each hosting their own copies of the communities they subscribe to, each providing their users their own hosting and defederation and moderation choices.
Beyond all of that, this is hopefully a situation that should get better when user-defined multi-communities come along. It seems to be a feature in the works, and should make it easier to keep track of multiple but similar communities. Other features have also been suggested for this issue, so you’re clearly not alone in finding it troublesome, which means hopefully it will get better.
IMO, simple user-defined multi-communities, whose member communities are easily sharable is the way to go.