The first step would be to edit your settings.json file.

Then you may want to install plugins, which can be done with the help of the plugin manager (https://<yoursite>/admin/plugins).

If you are running a production installation of Etherpad, you may want to store hashes instead of plain text passwords for normal and admin users. See for example: https://www.npmjs.com/package/ep_hash_auth.

You can also adjust the optical appearance of the index-page and of the pad itself. For this you will need some html and css knowledge.