It depends on context, but it could mean "If you do the thing you are thinking of doing, there will be bad consequences and so you will regret it."

It means you will be sorry about something or you will regret something. It basically means exactly what it says. There is no great mystery.

تُستخدم الكلمة One (ONE sorry individual) في هذه الجملة لتاكيد الكلام تعني لو فعلت شيئا، لندمت عليه ندماً

Do you understand all the words? Have you looked up synonyms for them? Presumably you know that "individual" more or less means "person". Do you know that "sorry" is an adjective that can mean either feeling apologetic or feeling regretful?