With the help of the periodic system chemists can predict properties of chemical elements and derive chemical reactions. But you need not be a chemist to understand the periodic system.
First of all the question arises: What is a chemical element?
Chemists of the past noted here: “A chemical element is a chemical substance that cannot be further broken down into other substances.“
All known substances are formed by these elements. At present (2017) we know 118 elements. The elements 113, 115, 117 and 118 were added most recently in 2016. They belong to the so far 27 elements which cannot be found in nature but are man-made. Many of the remaining 91 elements are found only in the form of chemical compounds in nature, not in their pure form.