There are a few ways to do this. In engine, one of the users runs the game (Play in editor) as a listen server, the other user launches the game normally, opens the console with the ~ button and types open 192.168.1.155 (replace that with the ip address of the listen server)
alternatively, package the game, this creates an executable of the game you are working on. From here create a shortcut to the exe file and add the following to the end of the path:
?listen -game
this will cause the game to launch as a listen server
so for me the shortcut was D:\Builds\WindowsNoEditor\TitanGame\Binaries\Win64\TitanGame.exe ?listen -game
if you are using hamachi, that will assign you an ip address, if you cant find it displayed on hamachi, open up a command prompt and type ipconfig /all this will show you your ip address assigned to your pc. Look for the IPv4 address
Have a read of this too:
You may find that when a player connects, they are not spawned in with a character, this is more than likely due to not enough spawn points / unblocked spawns, either add more, or move players away from the spawn point. This is an issue I was having when first starting to get networking behaving.