Going from the short bare boat mast to a rigged lateen sail takes a bit of thought. The lateen sail is a triangular sail that that has a spar tied along its long side, with one corner, called the tack, secured to the bow -- the pointy end of the boat. At the top, up in the air, one corner is called the peak, while the lower, back corner, called the clew, of the sail is held in check by a rope called a sheet. The mast that carries a lateen sail is always shorter than the spar.
Lash the peak -- the "upper" corner of the triangular sail -- through the eyelet of the sail and through the hole in the spar with heavy sail twine. Lash the peak eyelet to the body of the spar with a separate lashing as well. Lash the remaining eyelets on the head of the sail -- the long side of the triangle -- to the body of the spar.
Tie a line to the tack end of the spar with a bowline and reeve the line, called a sheet, through a fairlead on the bow -- a single-pulley block used to change the direction of the pull on a line. Tie a second line through the eyelet at the lower corner of the triangular sail, called the clew. The tack sheet and the clew sheet are used to shift the sail as the vessel changes course.
Tie a line to the centre of the spar using a bowline knot. This line raises and lowers the sail and is called a halyard. Reeve the halyard through the head block near the top of the mast. Reeve the tack sheet through the fairlead on the bow of the boat and secure the end of the line to a cleat. Hold the clew sheet to control the sail. Pull the halyard to raise the sail.