How could I explain to my boy, on the simplest way present simple and present continius tens
Usually, the present continuous is used to describe something that is happening now, while the present simple describes something that happens regularly (or, sometimes, not at all).
There's more to it than that, but that's the simplest explanation.
A clue is if the sentence includes a phrase like "every day", or "sometimes", or "usually" -- anything that indicates how often something happens. Then it's the present continuous.
A phrase like "now", "at the moment" or "today" is a clue that the present simple might be best choice.