Before you even start to learn chords or songs, it is essential to first learn about the keyboard. The piano keyboard actually repeats its notes from top to bottom across several octaves. In other words, the notes change from low (left side) to high (right side), without varying in pitch. In total, there are twelve notes that a piano has the ability to produce: seven white key notes (C, D, E, F, G, A, B) and five black key notes (C-sharp, D-sharp, F-sharp, A-flat, and B-flat).
If one were to play the white key notes from C through B and back to C, it will create a regular eight tone octave scale in C major. If one decides to play the black key notes from C-sharp (next to the white C key) through B-flat, then it creates a pentatonic (five tone) scale. You can also play every key (both black and white) from C to C in order to create a chromatic or twelve-tone scale.
Normally, the piano is tuned for C major as it is the more common key. Regardless, other keys can still be played by mixing both black and white keys to get the proper sharps and flats for each note. Generally, majority of the keys seen in music sheets can be played on the piano, making the instrument a very versatile one. It is relatively simple to double-check a piano’s tuning by playing pairs of the same note at differing octaves. The notes should sound identical. If somehow they are not, then perhaps one or both of them is sharp or flat and would require to be re-tuned.
You can begin playing some notes, typically starting with middle C. All you have to do is to gently but firmly push down on a key to produce a note. Try repeating the act in various motions including slower and faster as well as softer and harder till you get an idea of the type of control you can exert over the sound of the piano. Also, without moving your hands, proceed to play all the ten notes under your fingers. You will eventually realise that some (such as the pinky) are much tougher to play loudly, whereas others (such as the thumb) would take practice to play softly.
Do play the black keys too. Typically, black keys are played simply by moving the appropriate finger up and to the right, except in the case of the thumb, since it would be quite a challenge to move the thumb up to play a black key without changing your hand position. From the middle C position, your pointer finger can move left and right to play C-sharp and D-sharp, respectively.