This is how to create self signed certificate using Windows PowerShell ISE. Self signed certificate is using when implement web client and mobile client in NAV. First download "GenerateSSCertificate.ps1" file using below link to create certificate. After downloading it copy that in to C: drive in public server (web client running server).
Then run Windows PowerShell ISE as a administrator and execute below script in public server. In this example 192.168.1.1 is the public ip address. replace your correct public ip address and excute the script. After executing script certificate will be install.
After executing the script go to MMC and check.