Hi, pavoo. You basically have two options.
First, your brother can use the main menu to connect to a game you host in the lobby by selecting Main Menu>Multiplayer>Join Game. You have to find your internal network IP address. You can run ipconfig(if you're on windows) from a command line and look for IPv4 address.Your brother should enter this in at the prompt and choose a nickname. You can bring up a command line by running cmd.exe.
Second, you and your brother can choose to play together in someone else's match.