Salt & Such

Hello!
I'm sorry if I'm putting this in the wrong part. I wasn't sure where else to put it. But I was wondering if anyone could tell me what things like Salt & Garlic do in aiding people with Supernatural beings? I keep hearing the obvious, like, Salt is for protection and a Purifier and the most obvious that Garlic harms Vampires but what makes these things do what they do? What else can they do, if anything? How would you use them? etc.

It probably seems daft to ask but I'm more curious than anything.

Martin