The periodic table represent the culmination of all of our understanding of the elements. It tells us more than just how heavy an element is or how many protons it has. It arranges all of the known elements into groups that show naturally occurring patterns. Elements in the same column will have similar chemical properties. Elements in the same row will have similar physical properties like atomic mass. This can even help scientists predict what properties undiscovered elements will have.
Dimitri Mendeleev is credited with the creation of the first periodic table. He looked at the chemical and physical properties of elements known at the time and noticed repeating patterns or "periodicity". He even left gaps in his periodic table to account for undiscovered elements.