Q: How do I make apache to use the domain ssl certificate? I've registered a domain and my hosting provider includes an ssl certificate for me.
I've set up the A dns redirection to the IP where I have a linux ubuntu VPS with an Apache server installed on it.
I've tinkered with self signed certificates and let's encrypt ones to set up the web ssl using the proper directives:
SSLEngine On
SSLCertificateFile <certificate chain file>
SSLCertificateKeyFile <private key file>

But now I don't have the cert and key files for my domain certificate so:
Is it posible to make the virtual host to use the domain? Do I have to download cert files and place them as I've done with the let's encrypt ones?

A: Of course you need the certificate files for TLS to work.
If your hosting provider includes a certificate, you should contact him about the key files.
Just upload them to your server and make sure to set proper permissions.
The configuration in apache works exactly the same as with your letsencrypt certificates.
