When we join staffs together with a brace at the start of the left side of the music we create a grand staff. This is useful for piano players as they can read both hands at the same time.
Why the gap between the two staffs? Notice that you only get to an E on the bottom line of the treble clef before running out of lines. What do you do for the next pitches?
Next notice that the top line of the bass clef is an A and then you run out of lines.
What about the remaining B, C, C#, D, D# shown below.
The solution is Ledger Lines
Ledger lines allow you to notate extra pitches above and below any of the clefs. Middle C for example can be written below the treble or above the bass clef by adding a small line.
If middle C is written on a ledger line below the treble clef you will play it with your right hand.
If the middle C is written on a ledger line above the bass clef you should play it with your left hand.
The notes B and D that surround middle C can also be written using ledger lines.
MORE Ledger Lines
You can even go up and down further adding extra pitches so you can notate ALL of the pitches found on a piano.