Rust is what happens when iron reacts with the oxygen in air or water. Most rust can be easily removed with a combination of abrasion (tinfoil) and corrosion (phosphoric acid, found in Coke).
Here's my bike, a 3-speed Electra. It's beautiful, but I carelessly left it in the rain a few months ago, and it's been rusty ever since.
Like, really rusty. It was giving me dirty looks as I walked past it every day.
So I decided to tackle it using only a small tub of Coca-Cola, and a wad of aluminum foil.
Dip the foil in the Coke ...
... And start to scrub away at the rusty bits. It's actually amazing how quickly it worked, with very little effort. Amazing and scary.
On the right is before, on the left is after. My thoughts as I was working ranged from "This is amazing stuff!" to "I can't believe I drink this stuff!"
Oh, I don't know what this is, but it was everywhere, and I'm pretty sure it stains clothes, so heads up. I kept a rag and a bucket of water nearby to rinse my hands every once in a while.
It took a little elbow grease, but eventually I got the whole thing sparkling. When I was finished I washed it with soap & water (like I'd wash a car) to make sure all that acid & sugar was gone.
Here's an after photo (I brought in Seamus the puppy for a cameo). I can't believe how great it looks! Who knew?!