Subnostr

Help me understand relays? I've got like 23 but most have zero posted to it.

If there are people that I absolutely want to see in my feed how do I figure out how to get that to happen. For instance nostr:npub15879mltlln6k8jy32k6xvagmtqx3zhsndchcey8gjyectwldk88sq5kv0n I don't see any of his unless I go to his profile. We have many of the same relays, but never see his stuff in my feed. There are others as well, just an example.

Thanks