The provisional cast-on has a variety of uses. It starts with a crochet chain on a crochet hook about the same size as the knitting needle. A chart is given below of crochet hooks that correspond most closely to knitting needle sizes.
To work this type of cast-on, start with a crochet chain one or two stitches more than the number of stitches to be cast on for the pattern you are working. Since the edge is removed to work in the opposite direction the chain should be made with a contrasting color.
Once the chain is completed, with a knitting needle, pick up and knit in the back bar of each chain until the required number of stitches is on the needle. Continue to work the pattern as given in the instructions. Instructions then indicate that the provisional cast-on be removed so the piece can be worked in the opposite direction. In this case, hold the work with the cast-on edge at the top. Undo one loop of the crochet chain, inserting the knitting needle into the stitch below the chain. (This stitch is on the original first row of knitting.) Continue to undo the crochet chain until all the stitches are on the needle. This provides a row of stitches ready to work in the opposite direction.