An element (in chemistry) is a collection of identical atoms. There are over a hundred identified elements and they have been (very conveniently) arranged in the periodic table of elements. There are a large number of naturally occurring elements and others are man-made. They can also be classified as metals, non-metals and transition elements or as radioactive and non-radioactive elements. Elements also form thousands (if not millions) of compounds (by bonding to each other in different ratio , through ionic or covalent bonds) of our use.
Examples of their use are everywhere. We use copper and aluminium as electric wires, glucose as food source, silicon as substrate for solar cells and computer processors, oxygen for breathing, NPK fertilizers, nuclear energy generation (by nuclear fission of Uranium), etc.
Hope this helps.