Fingering
Fingering for the organ is similar to fingering for the piano.  However, organists use a lot of “finger substitution” which means: changing to a different finger while a note is held down.  This is useful in music such as hymn tunes which have lots of chords.  It helps to make the music legato (smooth):  (a pianist can use the right pedal to make chords legato.)  An organist playing on the pedals also needs to decide which foot to use for each note.  This is called “footing”.  A v sign means: play with the toe, a square u sign means: play with the heel.  When these signs are placed above the note it means the right foot, below means for the left foot.