Question

What is the difference between a quarter note and an eighth note? How are the notes sung/counted differently

Answer 1

Quarter note has a filled note head. Single eighth notes can be connected into pairs by a beam.

Answer 2

When a quarter note is assigned the time value of 1, an eighth note will receive a time value of one-half. When two eighth notes are grouped together it is easy to divide the "1" in half and think "one and"in rhythm for the two notes