It is actually easy to participate in Lemmy from Mastodon. Federated community are represented as user. When someone write on the community, they appears as the author on Mastodon while the community boost the post. So Mastodon user follow community. By mention the name of community in a post that is not an answer, their write post. The next post in the Mastodon thread will be treated by Lemmy as comment. The problem is more in sharing comment. After one or two level or comment it is becoming very buggy. For the rest, it works very well.