In order to play the online mode, you will need to create an Asmodee.net account. You can do it here: https://account.asmodee.net/en/signin

Please note that you must link your Steam and Asmodee.net accounts in order to play online with your Steam friends. You can do that by signing into your Asmodee account and linking the two here: https://account.asmodee.net/en/profile/otheraccounts