The periodic table (periodic table of elements) is a chart of the chemical elements organized around some of their recurring characteristics. For example, the column on the far right is the noble gasses, which tend to react similarly with other atoms. The column on the far left are the alkali metals, which have one valence electron and tend to form singly charged cations.
The periodic table lists the elements in order from left to right and top to bottom, with significant gaps to make the properties line up. The gaps are a result of the way electron orbitals work. The lanthanides and actinides usually appear at the bottom of the table to reduce the width of the chart.