In music notation, a note value indicates the relative duration of a note, using the shape of the note head, the presence or absence of a stem, and the presence or absence of other features such as flags.
The Whole note is the longest music note in general use today. It is an open note with no stem. I always say to my students it looks like a hole…so it is easy to remember! The duration of the whole note is 4 quarter notes.
The Half note duration is 2 quarter notes. It differs from the whole note in that it has a stem, although it is still open. For students I liken this stem to the line in the middle of the ½. This also helps them remember that 1 half note is worth 2 beats (in 4/4 timing, which is what they are usually working in when learning this).
The quarter note has become the standard 1 beat music note. This has happened as the 4/4 time signature is the most popular (with 3/4 and 2/4 following close behind) and quarter notes have a duration of 1 in these time signatures. It is also roughly in the middle of the most used notes in the Rhythm Tree, making the quarter note the ideal candidate for ensuring whole notes don't become too long to count, and shorter, popular notes such as eighth and sixteenth notes aren't impossible to count in terms of them being fractions of a note. The quarter note changes from the half note as it is filled in, as opposed to empty.
The eighth note is worth ½ of a Quarter note. It may also be considered as a one beat note in 3/8 and similar timings, the 8 on the bottom of the time signature giving the clue that you are counting in eighth notes. This is the first note in the rhythm tree to have a flag. The flag is the name for the 'tail' added to the eighth note. Eighth notes may be a single as shown on the left, or joined together with beams.
It is common to see eighth notes joined into sets of 2 to make one beat. Eighth notes may also be grouped in 3s, 4s, 5s, or even 6s depending on the time signature. Remember, however, that no matter how many eighth notes are joined, each one is worth half a quarter note.
The Sixteenth note is worth ¼ of a Quarter note. It may be beamed together in the same way as the eighth note. It changes from the eighth note by having an additional flag. Look at the picture and you see a double flag at the top of the stem. This is how you tell a note is a sixteenth note.
Sixteenth notes may be beamed together in the same way as Eighth notes. When you see sixteenth notes beamed together each note has a double flag. Here is an example of 4 Sixteenth notes beamed together, they are also common in groups of 2.