The Grand Staff
This is what is known as the grand staff. It includes the treble clef and bass clef. Pianists read from the grand staff.
Note that the two notes shown above are the exact same pitch. Each is called "middle C."
Clefs in Relation to Middle C
Middle C is the note exactly between the bass and treble clefs, as noted in the image above. It is known by many other names, but for these tutorials I will be calling it "middle C". Middle C is located in a different spot for each clef, but it remains the exact same pitch. To show how each clef is related, here are images of each clef with middle C. Yes, this means that the clefs overlap each other.
The treble clef is also known as the "G clef." The easiest way to remember this is seeing that the clef circles the note G (second line from the bottom).
The image below shows where middle C is located on this clef.
This clef is also known as the "F clef." One way to remember this is that the line between the two dots is F (second line from the top).
Middle C is located on the first ledger line above the staff of the bass clef.
For the tenor clef, middle C is located on the second line from the top of the staff.
On the alto clef, middle C is located on the middle line of the staff.
The tenor and alto clefs are referred to as the "C clefs." Notice that middle C is located at the middle line of each of those clefs.
Why all of the clefs?
Each instrument has a range of notes that it can play. If every instrument read from the treble clef, for example, there would be a lot of ledger lines for lower instruments, which would make the music very difficult to read. Different clefs are assigned to different instruments based on the notes each instrument is able to play.