Its a box that allows multiple computers (and phones etc) to be connected to each other in a network

If a computer wants to go through the router and onto the internet, then the router keeps track of which connected computer, asked for what

Pc1 wants go to bbc.co.uk When it sends that request it keeps track that the response is passed on to pc1 , who requested it

And then pc2 and pc3 dont need to know about it

Your internet connection has some random IP adress but then your router also creates “local” ip addresses for the locally connected computers, usually starting with 192, or 10.

And if i recall ports are used so the pc knows which program on the computer, requested the data

So the “address “ might be 192.168.0.10:443

Where 443 is the port