Question: I was wondering, what are the notes on a piano?Lily (Corpus Christi, Texas, USA)
Albert's reply: I assume you're talking about the names of the keys... but they don't really have names!
The most important concept to grasp is that the keys are not the notes.
There are many possible musical notes, and each of them is played by one and only one key on the piano.
However, there are several notes per key: Each key corresponds to several different notes.
If you listen to the two examples on the Piano Theory page, you'll find that the the first three chords sound the same, but the third chord is actually "spelled" differently, which makes it a different chord—meaning the notes are different.
In it, there's only one note that's different: In the first example, that note is F. In the second, it's an E-sharp.
Now F and E-sharp are both played by the same key on the piano, but they're entirely different notes. They sound the same, but have different functions. They act differently in different musical contexts. They lead to different chords in these examples.
You don't need to understand the music theory behind this example—just know that these are different notes played by the same key, and that this is a very important concept (called enharmonicity) in music.