Notice that the black keys are grouped in groups of two black keys and three black keys. C is the white key that is directly to the left of the two black keys.
A full sized piano with 88 keys will have 8 C's in different octaves.
As you play the white keys moving right from C you will go up the musical alphabet: C, D, E, F, G, A, B, C, etc. As you play the white keys moving left from C you will go down the musical alphabet.
The black keys make it possible to play notes with accidentals. A flat (♭) will move the note one key left and a sharp (♯) will move it one key right. In most cases that will move you to a black key, but in two places there are white keys without a black key in between. These occur at B to C and E to F. In those locations an accidental can move you to another white key. For instance, a C-flat is the same key as a B and an E-sharp is the same key as an F.
Double sharps (𝄪) and double flats (𝄫) move the note two keys right or left. So an F-double-sharp will be the same key as a G and a C-double-flat is the same key as a B-flat. When two different pitch names describe the same piano key, they are said to be enharmonic.
Middle C (C4) is located one ledger line down from the bottom of the treble clef.
Middle C is the C that is nearest to the middle of the piano keyboard on a full sized (88 key) keyboard. It is the 4th C up from the bottom of a full sized (88 keys) keyboard. On smaller keyboards it is usually (but not always) the C that is closest to the middle.
The C located on the 2nd space from the top of the staff (C5) is the next C to the right on the keyboard.