The codes you find in MMBN4 are used in the Open Battle section of MMBCC. Input them in the Data page and they'll become opponents that you can face in one of the four tournaments along with other created navis.
In order to play any of these tournaments in the Open Battle section at all, you must have enough navis to fill all the slots available. You can use the Fodder Navi list available on Gamefaqs to do so. Those fodder navis are completely weak with no chip whatsoever so you'll usually end up facing the navis created from the MMBN4 codes and, therefore, win their chips which are quite valuable.
One of the codes in MMBN4, however, give you the Hubstyle chip once inputted.