How do I follow/subscribe to them on lemmy?

Lemmy currently doesn’t allow you to follow individuals. As kbin does, it is probably a feature we will see in the future.

For now you’d need a Mastodon, kbin or Calckey account (I recommend the last one).

How do I see lemmy from calckey ?

Search for a community just like you would elsewhere.

This place would be @fediverse, so you'd search that to find this place on the fediverse. Lemmy communities use the same format.

As far as I can tell, this would subscribe you to a user with the username "fediverse". I've already seen a user and a community both named "cat" on the same instance, so that could be a problem if calckey doesn't differentiate between @[email protected] and [email protected].