green scouring pad is what I use. There is also a black variety that is more abrasive (and a white one that is very mild, for keeping it polished once you have restored the surface). Start with the finest grade that will do the job. An old, used pan scourer that has gone floppy is less abrasive than a new one.
Name is "ScotchBrite"
only rub to and fro in the direction of the brushing, not across it and never in circles which will leave prominent swirl marks
Ignore BlooLoo.
Clean stainless steel protects itself from rust by a chemical reaction with air that leaves a protective film on the surface. Some chemicals strip this off and cause corrosion. Including salt, vinegar, chlorine and other acid products.
HCl is hydrochloric acid. it is produced by adding chlorine to water. Household bleach contains chlorine.