In order for the website to always open with https: // you have to create a file called .htaccess (including the starting point) and place it inside public_html or in the folder of the domain or subdomain that you want to load with the SSL certificate .
The content of the .htaccess should have the following code:
RewriteEngine On
RewriteCond% {SERVER_PORT} 80
RewriteRule ^ (. *) $ https://AQUI_EL_DOMINIO.COM/$1 [R, L]
Only replace AQUI_EL_DOMINIO.COM with the web address that will open with https: //, important each domain must have its own .htaccess file in its respective folder
If your website is designed with wordpress, it is best to just install the Really Simple SSL plugin
You can see a tutorial here: https://youtu.be/2ssLdyP9an8