#6: Try Nmap : Zenmap GUI

Run Nmap - Zenmap GUI
*learn how to install Nmap -Zenmap GUI, click here

Target :  website domain name
Profile : Regular scan
Command : nmap [target]

Give it  a try 

Target :  www.atc123.xyz
Profile : Regular scan
Command : nmap www.atc123.xyz

Result
> 1000 ports scanned , 998 filterd
> port numner 80; open; http
> port numner 443; open; secured http

Try

> nmap -p 80,443 -Pn www.atc123.xyz 

Result 

> compare result
> direct scan port 80,443
> faster scanned result ( 0.69 second compare to 164 second)

Happy trying

*notes
-p = scan selected port
-Pn = treat host as online

others options refer here