Help with border

How-to Questions
1

Needing help with the last part of my right front border for a baby cardigan (Sirdar 4779 pattern)

Managed to pick up 23 sticthes ok and completed the first row for the pattern of 1x1 rib but stuck on the next part:

Rib 3, cast off 1 st (rib 4, cast of 1 st) 4 times, rib 2.

What does rib 3 mean?

Many thanks

2

It means you rib 3 stitches so either k1, p1, k1 or p1, k1, p1

3

Thanks

After rib 3 do I then knit/purl next stitch then cast it off or do I cast off the 3rd stitch in rib?