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 if the domain is the main one and if it is an additional domain in the folder of the domain
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]
You can see this video tutorial for it: