Whether it's used to bind objects or as an aid in climbing, rope is simply fiber twisted together. You can make rope out of a variety of materials. Traditionally, rope was made from hemp because of its strength and cohesive properties, but you can also make it from nylon or even grass. Most modern rope is machine-made, but it can be produced at home or out in the wilderness, too.
Select a fiber that can be twisted together into longer lengths. Almost any material will do. Take two strands and twist them together. The process is very similar to making thread. The longer the initial length of the fiber, the easier it is to make the original strand or yarn. Short fibers will need to be continually joined together to make a piece of decent length. Continue working with your fibers until you get a piece of usable length. The length needed will depend on your circumstances.
Keep the twist tight. You might want to secure one end to something and walk away backwards with the fibers in your hands. Keep twisting as you go. Old-time rope makers used a ropewalk, a long open area for twisting yarns and rope. Once you've finished with one strand, make another. The more yarn you use, the stronger and heavier your rope will be.
Take two lengths of your yarn and begin to twist them together. Twist them the opposite direction of the original yarn strands. The reverse twist prevents the original yarn from unraveling. Two yarns twisted together are called a marline. You can twist marlines together to make even larger ropes or cables. Large cables will probably require the use of some leverage. You might try a wheel that will turn the individual ropes.
Keep your ropes taut at all times. Kinks and loose yarn will ruin the rope. Pull as hard as you can while twisting. A well-made rope possesses amazing strength though made of thin individual fibers. Metal cables that support suspension bridges are made in much the same way. Experiment with materials, as some make better rope better than others, but in a pinch out in the wilderness, you can even make rope from shredded bark.