1. Turn on Wi-Fi
2. Go to Settings > About phone - it's usually on the bottom or on the last page of Settings.
3. Here, choose either Status or Hardware information. In one of these screens, you should find your Wi-Fi MAC address.

(Screenshots courtesy of Silicon Hill)

Send it, please, to our e-mail admin@sin.cvut.cz. Also, please include what device are you registering. Alternatively, visit us in LAB during office hours.