Turnbuckles are designed to make adding or releasing tension in a cable an easy process and without adding undue stress onto the coupling eyes of the cable attachment. Turnbuckles may be used to adjust the pressure on wood supports to level and straighten concrete forms. No matter what kind you use--the one made for cable or the one designed for wood--how you use turnbuckles will be exactly the same.
Attach the cables ends to the two eyelets of the turnbuckle using the appropriate clamps and cable inserts. If you are using a turnbuckle on a wood support, make sure both ends of the turnbuckle are nailed down firmly.
Connect the cable ends (or wood support ends) to the anchor and the object to be supported. Make sure the turnbuckle is placed so you can easily reach it.
Place the claw of your hammer in the middle section of the turnbuckle (which will look like a metal loop with two threaded screws entering it). Using the hammer, turn the turnbuckle clockwise to tighten the tension of your supports or counter-clockwise to release tension.