I don't understand the pattern! Help!

can someone tell me what the bits in round brackets mean please? I’ve not come across them before. This is only my second attempt at knitting so I’m no expert. Many thanks. Tracey

Welcome to KH!
The parentheses in row 8 indicate a repeat. For the circled size (great idea to circle this), the directions for the repeat are to (rib5, rib2tog) 9 times across the row. So you should work rib 5, rib2tog, rib 5, rib2tog, rib 5, rib2tog, etc