How To Tie a Square Knot 

So you're ready to Tie The Knot, here's one you need to know.
The reef knot or square knot consists of two half knots, one left and one right, one being tied on top of the other, and either being tied first...The reef knot is unique in that it may be tied and tightened with both ends. At sea it is always employed in reefing and furling sails.
But under no circumstances should it ever be tied as a bend, for if tied with two ends of unequal size, or if one end is stiffer or smoother than the other, the knot is almost bound to spill.