re: Cast iron rusted after first use?

Wipe it down with a film of vegetable oil and put in oven at 400 (500 seems high to me because it will smoke the oil). After 20-30 minutes, turn off the oven and let it cool, then remove the skillet. Do this several times if you like over then next few weeks. It will get better each time you cook in it. That just looks like bacon residue to me and no problem.

You need to season that skillet more than you have is the main problem. They need to get blacker than your skillet is