Atomic number along the bottom, the property you choose up the side. The vertical lines sit at the noble gases, which is where one period ends and the next begins.
The panel names at the top right open and close each panel. Choose the vertical axis in the property panel and switch between joining by period and by group. Drag a panel by its header to move it.
With ionization energy the line peaks at each noble gas and falls to a trough at the alkali metal that follows. With atomic radius the peaks and troughs swap places. A property repeating like this, purely from ordering the elements by atomic number, is the periodic trend.
Join the elements by group instead and you read the columns. Down a group the ionization energy falls and the radius grows, because each step down adds another shell outside the last.