Like the strings of the guitar, letters are used for music notes.
This is called the musical alphabet.
This is a musical note called a quarter note (or crotchet). It lasts for one beat or count.
On a piece of paper, copy the following diagrams and then trace the quarter note stems going up, as well as the barlines and the double bar line.
Draw your own stems going up and trace the barlines and the double bar line.
Play these two exercises on the second string (B) after you have completed the tracing. Remember to use i and m and to use the rest stroke.