A MAC address names the network card. It is burned in at the factory. It says which card, and nothing about where the card is right now. Nobody delivers mail to a serial number. So every device gets a second address that says which network it sits on. That is the IPv4 address.
An IPv4 address is a 32-bit number. Humans write it as four numbers from 0 to 255 with dots between them (dotted decimal), like 192.168.10.2. The machine never sees the dots. It sees thirty-two ones and zeros. Each of those four numbers is an octet: eight bits, which is why no octet ever goes past 255. The front of the address is the street (which network). The back is the house number (which device on that street). Routers care about the street.
Basically, MAC is identity of the hardware; IP is location on the map. Floor two never leaves the building. Floor three is the address that does. Everything that sends or receives a packet needs one: laptops, printers, phones, cameras, and managed switches (so you can talk to the switch, not so it can switch). A Mac address names the card. An IP address names where it is.
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