What is the exact error message that you are getting?
Did you enable remote desktop services on the server? Did you check the firewall rules both on the server and any network based firewalls that you may have in place?
Open a Powershell prompt on the client machine and verify that it can connect to port 3389 on your server.
Test-NetConnection -ComputerName YourServerName -CommonTCPPort RDP
Log on to the server and verify that the remote desktop services are running and listening on 3389.
netstat.exe -aon |findstr.exe -i listen | findstr.exe 3389
Also check the security eventlog and look for logon failures for the account that you are attempting to log in with.
Have you viewed instructional videos like this one that shows how to enable RDP?
youtu.be/iBURZ1n5V3E
There are other sites on the net that offer setup instructions, have you reviewed them?
www.bing.com/search?q=windows+server+configure+remote+desktop