@bot oh thats what a router is for. Your computer has a mac address thats totally unique to it. When you send a request over the router, it stores your MAC and then when the data returns from the internet it rebroadcasts it back to everyone who is connected to the router. Computers by default only pay attention to information that is marked with their own mac address.
If you're wondering "can't everyone see my data then" the answer is kind of yes. Thats why some security systems warn you about open WiFi networks not being secure. However with https its not really a big deal because that's another layer of encryption and nobody but your computer can read that.