The OP has a kbin account, which is something akin to Lemmy. But they can comment here because both kbin and lemmy are a part of the fediverse and therefore are interoperable.
But within lemmy itself, you can also have accounts on different instances too! E.g. my account is on lemm.ee, while yours is on lemmy.world. Both servers are a part of Lemmy, but act separately, and are interoperable!
Think of it like email.
Kbin is like gmail.com, lemmy is like outlook.com. Users on gmail can send and receive emails from outlook, and vice versa.
Now think of lemm.ee as outlook.co.uk, and lemmy.world as outlook.co.ca.
Lemmy is a part of the fediverse.
The OP has a kbin account, which is something akin to Lemmy. But they can comment here because both kbin and lemmy are a part of the fediverse and therefore are interoperable.
But within lemmy itself, you can also have accounts on different instances too! E.g. my account is on lemm.ee, while yours is on lemmy.world. Both servers are a part of Lemmy, but act separately, and are interoperable!
Think of it like email.
Kbin is like gmail.com, lemmy is like outlook.com. Users on gmail can send and receive emails from outlook, and vice versa.
Now think of lemm.ee as outlook.co.uk, and lemmy.world as outlook.co.ca.
I hope this clarifies stuff a bit!