A common question about Mastodon is the difference between favourites and bookmarks:
⭐ Favourites are the "likes" of Mastodon. If you favourite a post, it lets the author know you enjoyed it and adds your username to the "favourites" section below that post.
🔖 Bookmarks are a private way of keeping track of posts you want to go back to later. When you bookmark a post, no one else knows about it. Bookmarking just adds the post to your own private list of bookmarks.