First of all, you will need a coaxial cable of length 100 inches. Using a sharp edge, strip the outer insulation material from the wire. Then, grab yourself a coaxial cable metal braided shield (items like these can be found at various hardware stores) and pull it down your coaxial cable wire so the two lengths are parallel. Find the hole in the braided shield and guide the wire through this, until around half the wire has been passed through. Attach antenna insulators to the ends of the coaxial cable wire. Tie the ends together and you should have a large loop formation.
For your CB antenna to receive signals, it will need to be located at least 20 feet above ground level. The best way to achieve this height is to tie a rope or non-metal wire structure to your antenna and haul it up a tree or up the side of a building. The remainder of the wire (that is coming out of the loop) should hang down to ground level, in order for you to plug it into your CB radio. With a little bit of luck, you should now be able to tune into the CB radio station! Bear in mind that as your antenna is homemade, the signal and there quality of transmission may be poor - so whilst building a CB antenna is fun, it may be better to buy an antenna to use in the long run.