The multiplayer doesn't work like at all,
in order to see other servers you need to be on the same network as the host, if you are on the same Wi-Fi, you'll see their server. if you are on separate networks you can use a vpn to act like you're on the same network. if you're a bit more tech savvy you can forward port 1777 (i think this is the default port used by unreal) and your server will be discoverable by anyone else, i would suggest using a vpn however there are plenty of free ones that do just hosting a network online. i hope this helps, do let me know if you need any assistance!