What does this mean

K and inc 1(dec 1: dec3) sts evenly across row

The instructions in () are for different sizes. If you’re making the smallest one, K and inc 1 st evenly across row - like in the middles. If you’re making the middle size, dec 1 in the center, and if you’re making the largest size, dec 3 sts evenly spaced across the row.