You can now edit `/etc/nginx/sites-available/mastodon` to uncomment and adjust the `ssl_certificate` and `ssl_certificate_key` lines.
Then, reload nginx for the changes to take effect:
```sh
systemctl reload nginx
```
This will obtain the certificate, automatically update `/etc/nginx/sites-available/mastodon` to use the new certificate, and reload nginx for the changes to take effect.
At this point you should be able to visit your domain in the browser and see the elephant hitting the computer screen error page. This is because we haven't started the Mastodon process yet.