this is a simple and useful hitch that I learned so long ago that I don't remember learning it. It is easily adjustable and easy to release. It's really just a series of three half-hitches, but the separation between the first and the other two is what makes it work. If you slide the first hitch along the rope toward the others and then slide the pair away from the first, the line bearing the load will be pulled taut. Go the other way, slide the two hitches toward the single one and then the single one toward the stake or whatever that the line goes around and you put slack in it. Since the two half-hitches never carries a heavy load, it will not bind up and is easily undone when necessary.
First the line, which is already attached to the load at the other end is passed around the tent stake, tree limb, tie down point on a trailer or whatever, then brought back to a point at least several inches from the stake. The first half-hitch is tied here and then the free part of the rope is lead parallel to the standing part for about a foot more. The distance between the two parts of the knot isn't critical. It must be large enough so the two parts can be slid toward or away from one another in order to adjust the tension on the load.
Next, The two half-hitches knot is tied around the standing part keeping the distance between it and the first hitch.
Step 3: Tightening the Knot
To tighten the knot (increase tension on the load) pull the rope between the stake and the half hitch toward the half hitch which is then slid along the standing part toward the two half-hitches. Then slide the two half-hitches along the standing part to take out the slack this has created. Repeat this process until the desired tension has been achieved.
Step 4: Loosen the Knot
To loosen the knot (reduce the tension on the load) just reverse the process. First slide the two half hitches toward the single and then slide the single toward the stake.