In order to connect your machine to the network, the administrator requires the MAC address of the machine you wish to connect. The machines (and more particullary the laptops) can have multiple mac address. Indeed, a mac address is associated with an Ethernet Network interface (RJ-45 wire), or Wi-Fi (wireless).
Most of the time, a mac address is like xx:xx:xx:xx:xx:xx and is only written with hexadecimal characters, from 0 to 9 and from 'a' to 'f'. (for ex, 36:e2:5f:88:12:1a is correct) Sometimes it can also be like xx-xx-xx-xx-xx-xx (on Windows for instance) or xxxxxx-xxxxxx (more rarely).
Actually, only the wired network is deployed (the deployment of Wi-Fi is in study, if you want to participate), so the only MAC adress we need for the moment is the Ethernet MAC adress.
Here are some tutorials to help you to find your MAC adress on different systems :
(We are about to translate the tutorials but it takes time)