i couldn't understand the Initialize part should i put the ip address in the first parameter instead of autodiscover ? or i should Initialize udppacket to subscribe ?
You don't. By default, all IP addresses on the computer you are running this on will listen on the given port. See documentation (https://www.b4x.com/android/help/network.html#udpsocket_initialize) to see what the parameters are for UDPSocket's Initialize method (the IDE should provide you with the same information).