The launcher has been updated to allow you to log in through Steam, removing the necessity to create an account. Now, you can simply choose a username and start playing!
You can also set an optional offline password that allows you to log in without Steam and without a network connection. In this offline mode, you will log in directly to the game servers (which will be automatically hosted by you or someone else on the local network as soon as you/they select a savegame) and therefore need to set said offline password.