Hello!
You have to add the package and extension name. You can find a lot of extensions here: https://flarum.org/extensions - Be sure to install someone compatible and updated.
If you, for example, want to install this one: Fof Links - https://flarum.org/extension/fof/links - That allows you to add links to the navbar, you have to add, in the Extension Manager this:
fof/links
You can find this name in the description of the extension where it says:
composer require fof/links
You only add the name. 🙂
Regards,
