Odd sections of rope make wonderful dog toys and can be as simple or as complex as you want to make them.
The simplest version is to take about a foot of rope and then tie a knot in the middle. You should really secure the knot in the rope by having two people hold a pair of pliers and use them to pull on each end of the rope and get that know as tight as can be. A second knot on top of the first makes for a sturdier toy and gives your dog a good place to grip it.
A knot on each end of the lench of rope makes a fun tug toy and you can make these out of different lengths.
You can also take a longer length of rope, about 2 feet and tie the ends together to make a loop. This is fun for dogs who like to play tug-a-war and especially works great if you have a couple dogs that like to play tug-a-war!