Hi

A Molecule of a substance is defined as the smallest possible unit of a substance having all the physical and chemical properties of the substance. It is usually formed by two or more atoms coming togather to form a smallest identifiable unit

This molecule are formed when atoms come together to form chemical bonds which are generally formed by sharing or donating electrons between the atoms. There are different types of bondings like

Ionic

Covalent

Hydrogen bonds

Van der walls interactions

Hope this helps