Usually, there's a biggish grommet at the tack and the clew: you can run one or two lines here to get the reef in. To keep it in, you need to secure the bunt (the loose foot of the sail) and this means tying reef knots at four or five point along this part of the sail with relatively light line.
The choice of single or more reefing lines is a function of friction, the desire to not go to the mast in heavy weather, and skill set. Some have tack hooks, others don't. I prefer them, but it means a trip to the mast.