First, I would like to point out that I happened to have extra fence panels that matched my current fence. If you do not have extras, you should not have any problem finding panels to match the type of wood your fence is in. However, if your fence is constructed of the narrow type panels, let us say 1 in. x 4 in., you will want to buy wider 1 in. x 6 in. panels so as to be sure the ugly metal fence poles can be covered. Narrower panels would most likely not be able to enclose the poles.
All you really need to do is take 3 of the panels and make a 3-sided open box to cover the ugly metal fence poles with. Lay the 3 panels on a flat utility table or any flat surface. Lay one of the panels flat (this will be the front side panel), and secure the other two to each side of it to form your open sided box. Using a screw gun, or electric drill with a screw bit on lower speed, secure the 2 side panels using any wood screws long enough to secure the panels solidly.
To secure your wooden 3-sided pole covers to the existing fence, you will want to use L-shaped metal brackets. These come in various sizes and can be found at any home and garden store. You can place the newly made pole covers over the ugly metal fence poles to fit, and secure your wood covers to the existing fence, therefore enclosing your ugly metal fence poles. I then adorned a couple of my new wood covers with solar lights. You can hang plants, or whatever else fits your fancy. Some of the poles are covered by Potato Vines rather than the wood covers. I thought it would break up the pattern a bit, add some variety to the fence, and bring a nice lush appeal to the backyard.