WTF.. It's kinda messy for me.

So there are 4 computers, each 2 connected to 1 switch, both of the switches are connected to 1 router, now let's say
PC1 and PC2 are connected to SWITCH1
PC3 and PC4 are connected to SWITCH2
SWITCH1 and SWITCH2 are connected to a router
PC1 wants to send a message to PC4, PC1 needs PC4's IP address and MAC, PC1 notices that PC4 is on a different LAN, so PC1 sends a message to the router via the switch to ask who is PC4, packet is basically "who is" and "data", so by that I understand that PC1 asks:
who is - PLZ EXPLAIN THIS
data - what's the mac??

shit it got messy at this part.. can someone explain what the PC basically asks from the router?

I know after that, that the router looks @ his default gateway (?) and sends to that network LAN AND WTF IDK THIS SHIT... TO MESSY