You’ll get it in no time. The best way I’ve seen it described is email. You can have outlook. I can have Juno. Our pal can have aol. But we can all still talk to each other and see the same emails just as tho we all had the same email provider. Same thing here with instances. They’re each like an individual Reddit but we can all see them (for the most part, some have been blocked by others, etc.) And comment in then from our own instances.