Welcome to KH!
The numbers in the parentheses refer to the different sizes. Decide which size you want to make based on the measurements at the beginning of the pattern and then circle that size and the directions for that size throughout the pattern. So for this row, you would bind off the stitches indicated for your size.
There's a Glossary tab at the top of the page that will help with definitions and videos but come back here if you have questions.
This sweater comes in a very large range on sizes but it's very cute.