To begin we need to find a way to secure your hammock to a few trees that have a good distance. Keep in mind you are making a hammock for yourself and possibly others, take this into consideration when choosing your space. I used some scrap wire, and some cow bones from Ribeyes to anchor mine while building. Later while sleeping on the hammock one of the bones broke so I switched to the Hammock Straps shown in the instructable here
First we want to pick two of the best pieces of rope you have. Choose pieces about three feet (one meter) long. We will be tying two bowline knots in each of these ropes. One small and one with a very large loop. The small loop will connect to the tree and the large loop will connect to the long ropes (cords) of your hammock.
Tying a bowline:
1. Twist a loop into the rope a little more than twice the length of the loop you want to tie in the end.
2. Wrap the loose end of the rope around and tuck it under then through the loop
3. Wrap the loose end of the rope around the back of the body of the rope
4. Tuck the end of the rope through the loop again
5. Pull really hard and the knot will tighten up
About the bowline: Bowline knots are really secure. They are easy to untie, but will not come undone or slip if you do not want them to. It´s a great way to put a fixed loop in a piece of rope or string and is useful anywhere loops are needed.
Photos 2-5 are the bowline tying process, photo 6 is the desired end result.