Many tubular beading stitches begin with a ring of strung beads called a "base ring." You stitch into that ring to start building the tube.
With some stitches, you create the base ring by picking up a set number of beads, bringing the first and last beads together, and tying a square knot with the beading thread.
Other times, it's better to avoid tying a knot because the beads need to remain loose to accommodate space taken up by the first round of stitched beads. In those cases, you can create the base ring by bringing the first and last beads together, passing through the first bead again, and pulling the thread taut.
Tip: Occasionally, a base ring is made up of ladder stitches, rather than strung beads. You create the ring by stitching from the end of the ladder into the first bead of the ladder. Tubular herringbone stitch uses this approach.