I am not sure I understand what you're asking. A MAC address is a unique address or "identifier" assigned to your network device when it is in production.
But when you're on a network, such as your home network or school network, for packets etc to travel to their destination they need to know where to go, so they find their destination essentially through IP address.
The way it works is:
You, the client connect to the network.
You request an IP address from the router
Router gives you an IP address and stores what MAC address is assigned to that IP address
When data comes through that is destined to you, it checks it up with the router and sees what MAC address is asgined to your IP. Data delivered!
There are many ways to essentially "change" or "spoof" your MAC address. As always Google is your friend for such tools, I use "mac changer".