There are three printing styles: normal, condensed and 'chords only'

The normal style prints pretty much what you see on the screen displaying 15 chords per page:

The condensed style prints 'chords' consisting of just a melody note in a single line.  The keyboard is not shown.  Therefore it prints more 'chords' per page, uses less paper, and some people actually find it easier to use to learn new songs.  It looks like this (same song as above):

Lead sheet music as found in fake books consist of melody lines and chords.  Usually each bar has several melody notes and one chord name to identify the chord to accompany the melody line in that bar.  That's why the condensed print style works.  If there were only melody notes you could not easily identify the piano keyboard key to play.  Conversely if you had only chords (in the musical sense, ie. several notes played at once) the condensed style would look like the normal style.

To further help with identifying keys, the condensed style uses the following convention:

1)  if the corresponding key is a white key, the note is shown as an empty square

2)  if the corresponding key is a black key, the note is shown as an solid black square

3)  in either case if the melody note is a tied note, the color of the square is in a lighter shade of gray.

The figure below illustrates this.  Notice the rhythmic value displayed on the right margin