Picking up stitches

I am knitting a dog sweater and I am now getting ready to add the ribbing around the back opening and it says pick up stitches and knit. Then I pick up the loops that are sitting on my needle on the tail and then it says pick up and knit the stitches on the other side. I don’t understand if I am supposed to actually knit at the same time as I pick up the stitches or do I wait until I have all the stitches on my needle and then knit? Thanks for any help you can give me.

Pick up and knit implies a 2 step process but it can be done as a single step. Pick up by inserting the R needle into the st on the edge, knit by wrapping the yarn around it and pulling through the st. Some people like to use a smaller needle and working from L to R pick up all the edge sts and that becomes the L needle which you then knit the sts. But it’s much easier to pretend the edge is your L needle and just pick up and knit as you go across from R to L.