Understanding ARP

Hi all,

I apologize if this isn't the right place to be asking these kind of questions, if it isn't I'll remove my post.

Anyway, I am new to networking and am studying to take my Net+ soon. I am having some difficulty with understanding ARP, so hopefully one of you can help.

I understand the basic principle of it - a computer is trying to talk to another on the same network, but it doesn't know its MAC address, only its IP, so it sends out a broadcast asking for the appropriate machine to send back the MAC. What I don't get is how would the machine sending out the ARP request already know the IP address of the destination machine? Do computers automatically query all other machines on the network for their IP's, or are they possibly stored in an accessible table on the network? I would get it if the ARP request was broadcasted to every computer asking them all for their MAC, but I don't get how it already knows each individual IP on the network but not their respective MAC addresses as well.

Am I over thinking this, or is there something that I am missing? Thank you all for your help!