The value of a note expresses how long it is played. This duration is expressed as a fraction of a whole note. This is all based on the original notation of notes, yet these terms are still used in your DAW, e.g. when you quantize notes or select a grid for your editor.
The shortest note value is usually a 1/32 note, and 1/16 notes are the fastest notes in a melody. In case you have a many 1/32 notes in your music, it is an indicator that the speed of your music is too slow. By doubling the speed of your music, you can make the note values higher with no actual change of the length.
E.g. your melody is played at 60 BPM and has many 1/32 notes, it is probably better to double the speed to 120 BPM and use 1/16 notes.
Note Values in Digital Audio Workstations
As we do not work with music notation, but in a piano roll editor, note values and therefore their lengths are expressed by the actual length of the bar that represents the note.