Just wondering how I would play this composition as it has 3 staves (one treble and 2 bass clefs). Cheers
This is piano music: sometimes composers find it easier to lay out the notes on three staves rather than two, because in more advanced piano music there is no rigid rule putting the right hand notes on the top staff and the left hand notes on the bottom. In this case, the bracket on the second bar shows that the right hand plays all the note in staves 1 and 2; then the bracket on the fourth bar shows that the left hand plays staves 2 and 3 -- jumping from the low grace note to the chord.
In this case I think these could quite easily be combined in two staves, but it's the composer's choice, and we don't know what comes next.
In this piano pièce by Debussy, the three staves (as previously used by several composers during the 19th century, such as Franz Liszt) are there both to give more clarity to the composer's intent and ease the player's reading and interpretation. The clef used are just the most convenient at a given time. You can find examples with two treble clefs and one bass clefs.
To play this, just think about how you can split the notes between your hands, and where continuity (legato, melody) is required.
As already noted in other answers, vertical brackets group notes that should be played together by one hand (e.g. second bar, between the two upper staffs). Sometimes editors add such brackets when they feel there is an ambiguity or a technical advice useful to students.
In this relatively easy prelude (believe me, there are a lot more technically demanding ones in the book), the notation might look daunting but there is no 'transcendental' technique required.
The left hand has sometimes large horizontal moves to do, helped by the sustain pedals (e.g. 4th bar, first beat: a profound bass note shortly before the chord in the middle of the keyboard played by the left hand).
If this is an organ, the bottom staff is for the pedals and the octaves would tend to indicate that an octave coupler is engaged.
If the piece is for piano, the composer (or editor) has helpd a bit. There are some vertical square brackets here and there. I would guess that in measures 2 3, the top two staffs are played by the right hand, whereas in measure 4, the bottom two staffs are played by the left. I think the point is to make the music easier to read by spreading things out.
There is nothing here with a stretch of more than an octave, so it can be reached by most. extensive pedal use will be required, but that's down to the player - it's hinted at by the notes concerned - but unmarked. Probably written on three staves to make it clearer to read, and interpret.
There is also the benefit (?) of not having many ledger lines to read.