It is pretty simple to setup, so it seems likely that it's a config issue where the devices can't see each other, assuming you've set things up correctly, but let's start with the basics...
What are the systems you're trying to connect? and what are the IP addresses of each device? On your Windows PC (I'm assuming that's what you have), Do you have any firewalls turned on? Either the Windows Defender, or any of the 3rd party ones (McAfee, Norton, AVG, BitDefender, Malwarebytes, Avast, Kaspersky, etc)? What IP address did you put in the PC, and what address did you put in the tablet/phone? Do you have any firewall type apps on the tablet/phone?