Rust is a coating of iron oxide that occurs by oxidation, this is heightened in the presence of moisture on your object. It is usually seen in the colour red but also can be yellow-brown. Rust is most common on iron or steel.
How to prevent it
Keeping your metal dry is a good way of ensuring that your object stays rust free; for example, leaving your bike outside in the rain with no cover will increase its probability of rust occurring.
Applying primer to your metals is another effective way of keeping your stuff rust free! Primer acts as a waterproof layer than will ensure no moisture will reach the actual metal itself, therefore no oxidation can occur and rust will not be seen.
As an extra safe guard against rust if you paint your metal over the primer it will act as another layer of waterproof, which means if any moisture seeps past the paint it then also has to go through the primer. Applying primer and paint is the safest guard against rusting.
Placing dehumidifiers in your garage or storage room is another protector against rusting, due to the face that the dehumidifier will reduce the amount of humidity and therefore moisture in the air.
How to remove it
All these methods will not work on different types of materials, but in general people worry about rusting on metals themselves. White wine vinegar is a popular method to remove rusting on metals; this is because the white vinegar reacts with the rust and after leaving it in the vinegar the rust with form a paste you can simply rub off.
Sprinkling salt over the rusted area of your metal and juice a lime over the top of the salt is another technique in removing rust. After leaving it for a few hours again you can simply scrub off the rust from your metal. Little tip, if you use the rind of the lime you used, it is strong enough to rub off the rust but will not affect the metal underneath at all.