What makes stainless steel and steel different

Steel is simply iron with a small percentage of carbon. It oxidizes (rusts) easily.   Stainless steel has added chromium, but also may contain any of the following: nickel, niobium, molybdenum, or titanium.   Stainless steels form a very thin layer of chromium oxide on the surface which protects it from further oxidation. While stainless is not stain-proof, it does stain less than carbon steel.  Most stainless steels are non-magnetic, or very weakly magnetic.