Double vertical line means the beginning or end of a section of the song.

Single vertical line means the end of a measure of music & the beginning of the next measure (or count of 4 beats in this case because the song is in 4/4 time).

Double vertical lines with 2 dots ( ||:  [chords] :|| ) indicates to repeat the material in between the dots, essentially a repeat sign as in standard musical notation.

Hope that helps!