Final answer:
The note D is played on the open fourth string, and B is played on the open second string on a guitar. Both notes can also be found on other strings at different frets by shortening the string lengths.
Step-by-step explanation:
The note D on a guitar is typically played on the fourth string (counting from the thinnest to the thickest string), which is the D string itself, at the open position (no fret pressed). To play the note B, you would generally use the second string which is the B string, also at the open position. However, there are multiple places on the guitar neck where these notes can be found. For instance, the note D can also be played on the fifth fret of the A (fifth) string, and the B note can be played on the fourth fret of the G (third) string.
The frequencies of the open strings are important for understanding where these notes come into play. The strings vibrate at certain fundamental frequencies, which are the pitches we hear when the string is played open. The frequency of the D string is 146.83Hz, and for the B string, it is 246.94Hz. By shortening the string using the fretboard, we can achieve different pitches, including other instances of D and B on different strings and frets.