Are use cases just multiple user stories??
What are the benefits of using user stories over use cases.. and vice-versa... When to use one over other... Does all agile methodologies uses user stories??
Actually, the original use cases (see Jacobson's OOSE) were pretty lightweight, much as user stories are now. Over time, they evolved until a common format for "use cases" now is a complicated document with inputs, outputs, inheritance, uses relationships, pseudocode, etc. Programmers, in general, try to convert everything into programming.
In any case, the attempt to defined what distinguishes a "use case" from a "user story" fro a "scenario" is pretty futile, as it's hard to find two authorities who agree.\
Personally, I find the pattern "[Actor] [verbs] [noun] to get [business value]" helpful. If it gets over about a paragraph of text, it may be too big.