Understanding Pattern

Can anyone help understanding this. I understand how to decrease stitches. But I am confused on the brackets (7:1)
Dec row (WS): Rib 3 (7:1), p2tog *Rib 5? P2tog: rep from * to last 3 (7:1) St’s, Rib to end (72 (80:88) sts)
Many thanks, I’m new to knitting and find it such a mind field

Welcome to KH!
The pattern is likely written for 3 different sizes. Rib 3 for the smallest size, rib 7 for the middle size and rib 1 for the largest size. The same goes for the final stitch count, 72 for smallest, 80 for middle and 88 for the largest size.
What is the name of your pattern?