Are you trying to access the webserver internally or externally?
Internally means using a your lan/wifi without going through the internet using a private ip address range. Externally means using your public ip address or DNS name to connect to your webserver.

If internally you should be able to access the webserver using its internal ip address(192.168.x.x, 10.x.x.x). No changes required at the firewall at the router. Just need the necessary inbound rules at the web server.

If both of your devices is using wifi to connect to each other, it is possible that you wifi access point is configured to block wifi to wifi communication. If you can't ping each other, it is possible that it is blocked either by the access point or the firewall within the devices.

For connecting from the outside, you will to do some port forwarding on your router. Best to test using a different internet connection since not all routers allow traffic from the same internal network to come back in via port forwarding. It may work with newer routers so results may vary.

Also if your ISP doesn't provide you with a public IP address, you won't be able connect to your webserver from the internet.