That means this group of eighth notes must sound evenly over 1 beat.
Eighth notes subdivide (or evenly divide) the beat. We say “1” for the first eighth note and “&” for the second eighth note.
If you’re tapping your foot to the beat while counting, the first eighth note will happen when your foot is down (on a number).
The second will occur when the foot is up (on the “&”).
It is common to see eighth notes beamed together in either groups of 2 or 4. Don’t worry too much about this. It’s just a way of organizing the notes to make it easier to read.
Now, let’s talk about what to do when we see one single eighth note all by itself.