Setting up ssl and dynamic dns from own domain


This newbe needs help with securing my nextcloud.

I have a Pi 4, a private domain with cpanel ( and a ZTE modem.

On my Pi, Nextcloud is running fine. I set my modem to forward port 443 to my Pi. On my domain I set up a Dynamic DNS witch sends me to my Pi in my home.

Everything works, but it is not trusted. And there begins my quest.

I understand that for security I should use https and ssl certificates.

In cpanel i can view the ssl ‘Certificate’, 'Private Key’ and ‘Certificate Authority Bundle’ which are part of the dynamic DNS. They are not download files, but I see the funny text in a textbox.

Q1: should i just copy the text and put them in a textfile?
Q2: should the files have special names? or extensions?
Q3: where should I put those files?
Q4: do i forget something to make it work?

All the help is appreciated