@Reverendender to clarify, I subscribed to a lemmy /c (what's that called, a SubLemmy?) in mastodon, using my mastodon account.

@boby_biq you go to a feed (channel? sub?) in Lemmy, and copy the sub's address into the search of mastodon. (replace the ! with @)
in this example, take "!nathanwpyle@lemmy.world" and paste it in mastodon as @nathanwpyle