If you are in the same wifi network and are the server, you select a game and choose to start the netplay server. You wait for users to connect then start the game. For clients in the same network you choose to connect to a netplay server with the same game, as long as you are in the same wifi network clients will be able to see you automatically.
When the server starts the game, the game will be started automatically for all players.
If you are trying to play over the internet, the setup is a little different. Clients will not use you automatically, instead you will need to obtain a code from the server setup and give that to the clients. Once the clients enter the code, they will be able to see you and connect to you. Obtaining a code will fail if you don't have WiFi or if your WiFi router did not properly support UPnP
