Right in the middle of the piano staff system is C4. All the other Cs are arranged symmetrically around C4.
The treble clefs´ starting point marks G4. it is located on the second line (reading upwards).
The bass clefs´starting point marks F3. It is located on the fourth line (reading upwards).
The image above shows most of the notes you can play on a piano. The sequence of the notes (C-D-E-F-G-A-B) is repeated again and again. Those tones form the natural scale. The natural scale corresponds to the white keys on the piano while the black keys are chromatic (greek: Chroma = colour) tones. In order to receive those tones an accidental that either sharpens or flattens the notes of the natural scale has to be written in front of them.
The # sharpens the note one semitone higher. It is now called "original note name - sharp", eg. "C sharp".
The b flattens the note one semitone lower. It is now called "original note name - flat", eg. "D flat".