Ok, I just added a second line to my house for my home office. I have a two line phone and I am using the second pair of wires for the second line going to my phone. If I am on my main line and someone tries to call in on that line while I'm on it, will it automatically switch to the other line so I can use the hold feature?

No, that has to be set up with the phone company.
"Forward if busy", "forward on # of rings"

Or use "call waiting"

Or have it "rollover", done by phone company.