certbot will inform you where your files are stored (generally
/etc/letsencrypt). The files are locked own so you'll need to
sudo to get them. For me, my domain registrar required the following (see table below with what they required and what certbot files contained that information):
|Private Key (KEY)||privkey.pem|
Certificate Authority Bundle (CABUNDLE)
You should be all set once you've installed your certbot generated SSL certificate.
You'll likely need to reference this location (and the certs in there) in your application.
If you installed using the guide (specific to your system) from https://certbot.eff.org/instructions then automatic renewals will most likely be enabled by default (the instructions at the previous link will state this).
Referenced from the excellent openproject download and configuration guide here.