There are (at least) two ways to join this community if you come from other instances:

1. Go to the search of your instance (there’s an icon on the top-right), search for ‘miata’ (you might want to limit your search to communities) and from there click on the “MX-5 Miata” link.

2. Manually copy-paste the community name to your address bar. You need to add c/miata@lemmy.world to the address of your instance. E.g. if you are on lemmy.ml: https://lemmy.ml/c/miata@lemmy.world