Measure the height and width of the soffits with a tape measure.
Cut pieces of wood that equal the height and width of the soffits with a circular saw. If the soffit area is longer than the pieces of wood you are using, cut separate pieces to completely cover the soffit. For example, if the soffit is 12 feet long and you are using wood that only measures 8 feet in length, use one whole piece of wood and cut a second piece that is 4 feet long.
Place the wood on the soffit. Line the end of a piece of wood up with the end of the soffit. Use a nail gun to secure the wood to the soffit, placing a nail every 6 to 8 inches along the top and bottom of the wood.
Line up any additional pieces of wood with the installed wood. Press the end of each additional piece of wood up against the end of the installed piece of wood. Secure the wood to the soffit with the same process described in Step 3.
Cover the seams between the pieces of wood. Cut a thin piece of molding -- 1/2- to 1 inch in width -- in the same color as the wood to equal the height of the soffit. Place the molding over the seam between two pieces of wood and secure it in place with the nail gun, placing a nail in the top, middle and bottom of the molding. Cover all of the wood seams in this manner.