What is the difference between an inorganic and organic molecule?

Answer 1

It's arbitrary (and some chemicals are classed as both);
but in general organic contains carbon molecules and/or those related to life. It is the chemistry of carbon containing compounds.
Inorganic is everything else and generally do not contain carbon (with some exceptions).

Answer 2

Organic molecules contain carbon-hydrogen bonds and are typically found in living organisms. Inorganic molecules lack both carbon-hydrogen bonds and are often simpler in structure, like water or salt.