Hi Fiona,
Those are triplets! This means that three notes of equal length fit into a space where it’s usually two notes of equal length. Or rather, in this case, the half note is divided up into three equal triplets rather than two quarter notes. Counting triplets is a little difficult, as the second beat comes in somewhere in the middle of the second triplet. If they happen in the second half of a 4/4 measure, like in this piece, the first triplet is ON three, the second triplet is slightly before four, and the third triplet is just after beat four. Try playing it lazily, with feeling, and don’t worry too much about counting accurately, but make sure to continue in tempo with beat one in the next measure. It will feel natural after a bit of practice.
I hope my reply helps you rather than adding to your confusion! 😅