"How to cast on" is one of the first questions for any knitter. This long-tail casting on technique uses a single needle and produces an elastic knitted edge like a row of garter stitch.
Cast-on for Knitted Projects
Leaving an end about three times the length of the required cast-on, put a slipknot on the needle. Holding the yarn end in the left hand, take the left thumb under the yarn and upward. lnsert the needle in the loop just made on the thumb.
Use the ball end of the yarn to make a knit stitch, slipping the loop off the thumb. Pull the yarn end to close the stitch up to the needle. Continue making stitches in this way.