Hello ! 
I decided to host a website on Ubunto on port (80:) and everything works perfectly.
After that I decided to put ssl certificate. Everything was ok and the certificate was putted successfully!
When I try to open my website I recieved this error: Unable to connect to the server. But I can ping it ??
What is going on ??
I haven't enabled any firewalls. I have only opened port 80, no port 443.
My domain is: gogotih.com
I will really appreciate for someone's help !
Thank you ! 
Why? You specify it so specifically, so it seems you know port 443 has some purpose in this story.
No, it doesn't have any purpose in this story. I just mentioned if it can be a useful information.
It's very useful, as port 443 needs to be open, as it's the default port for HTTPS.
Can this be the solution for this ?
You have port 443 closed. It needs to be open. Your site doesn't work through HTTPS on its default port 443. Personally, I see the connection between the two.
I am gonna try this ! How did you check this, are there any useful tool or command ?
You told me yourself.
Also, I use cURL on my Linux system to connect to your site, which says "Connection refused".
Omg, thank you so much !!!!! 
Hi @Garjoman
so your question has already the answer.
No port 443 -> unable to connect your domain via https and the standard port 443.
@Garjoman, in case it wasn't clear from other people's replies, when you access http://a4osot.hopto.org/ the browser automatically connects on port 80 (even though you didn't specify a port number), while when you access https://a4osot.hopto.org/, the browser automatically connects on port 443 (even though you didn't specify a port number).
This different default port number has been provided by Internet standards for decades. I think it dates to 1995 or so, but the oldest authoritative reference I found right away is from 2000.
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