can you give me an explanation of sin?

The Word "sin" comes to modern English from Old English, and possibly before that from a Latin Word meaning "guilty".

In the most general sense, a "sin" (as a noun) is a crime or an immoral act regarded as a serious offense.

In it's original sense, it was (and still may be) more specifically used to refer to an immoral act considered to be a transgression against divine law.

In that way, the Word can now be used, usually informally, to refer to an actual crime against actual law, or can be used, often more formally, to refer to a pseudo-crime against an imaginary authority.