This Plugin's language is German and I dont plan to implement other languages as well.
You start with one (customizable) heart and you gain hearts for every 20 (customizable) advancements/recipes made.
If you complete every advancement/recipe your hearts will become 50 (customizable).
You can also see how many hearts others have.
commands:
/herzen for the GUI
/herzenvon <name> to see how many hearts others have