There is a subtle difference between the two words in my opinion. Redundant - something is redundant if the requirement or need for it no longer exists, so it is now unnecessary. Superfluous - something is in excess of the original requirement, so it is now unnecessary but the requirement still exists.

Redundant is relatively common but superfluous is not. I think most people would just say something is "unnecessary" or "unimportant" in place of superfluous.

Very good question. Both mean "excessive" or "unnecessary", but in usage they are not always interchangeable. For example, "He has been made redundant" - meaning he lost his job - cannot be changed to "He has been made superfluous".

redundant is used for something which is repeated unnecessarily while superfluous is used for things which are present more than enough.

More examples of the use of "superfluous" in daily life: - That remark of his is rather superfluous. - This pamphlet/report is badly written and full of superfluous detail. - Delete superfluous words from your essay.