Technically, pick up and knit is a 2 step process where you start at the other edge and pick up sts with the L needle, then knit them with the R needle. Pick up is a one step process where you insert the R needle into a stitch on the edge (pick up) wrap the yarn around the needle and pull it through the stitch (knit). Many people use the terms interchangeably. It's faster and easier to do the one step process, especially if you have a long edge to pick up on, or it's curved.
sue- knitting heretic