After installation cannot open discourse

I installed my community by standard installation and checked discourse-doctor, but there is no problem. But I cannot open my website.

Have any ideas?

Does your host name resolve to your server’s ip?

What do you see in /var/discourse/shared/standalone/logs/var-log/nginx/error.log (that’s by memory and typed on a phone, so you might need to direct something).

lots of "cannot load certificate “/shared/ssl/example.com.cer”: BIO_new_file() failed (SSL: err>

That usually means that let’s encrypt didn’t get a certificate. Don’t know if you tried too many times or if there is some issue with let’s encrypt. There has been a spate of people reporting problems. I can’t tell if it’s broken somehow, or it’s just bad luck.

Then should I change my domain? or change my instance?

You can try changing the subdomain name and making sure that the dns record resolves before you rebuild. Discourse-setup should check that the name resolves if you run it again.