Half hitch is a very simple knot, rarely used on its own since it is not a secure knot.
However, it is important part of various reliable hitches and knots. It is one of the most basic knots and one should really learn how to tie it, even with closed eyes.
How to tie a Half Hitch?
Tying is very simple. First, form a loop around the pole, object or by passing the rope through the hole. Pass the end of the rope around the standing end and through the loop. Tighten the rope carefully - since the modern ropes generally have rather slippery surface, if you pull too much, without tightening the rope properly, Half hitch can easily slip.
As said before, Half hitch is not secure knot and it should be really used only as a part of other knots.
In order to increase the holding strength and to tie a rope as fast as possible, two half hitches are often tied around the standing part of a rope.
This knot is known as two-half-hitches or double half hitch. It is much more secure, but if the rope was under larger load, it can be difficult to untie it.
In order to increase the control over the load while tying Half hitches, one can pass the rope around the pole or through the hole twice and then make two Half hitches - much stronger and safer Round Turn and Two Half Hitches knot.
Often, when rope is tying to the pole, after first pass of the rope around the pole, second pass is made. If the second Half Hitch is reversed, one gets Cow Hitch and if the second pass is in the same direction as the first Half Hitch, one gets Clove Hitch.
Often, to increase the strength of Clove Hitch, one or two additional Half Hitches are used.
Although rather simple, basic Half Hitch can be found in many knots and can be used in many situations.
Again, one must know it's weaknesses.