Begin by measuring to determine the location of the fence posts and marking each point with spray paint. The depth of the holes will vary, but leave at least four inches of clearance on each side of the post. Since the posts are 4x4, the added four inches on each side will require holes measuring 12" x 12".
Note: Do not space holes more than six feet apart, or the stability of the fence may be compromised.
When the holes are ready to go and excess dirt has been removed, mix up the concrete. Plan on using about half of a 90-pound bag for each post. Make sure the concrete is churning every couple seconds or it will become hard on the bottom and dry on the top.
Place each post in a hole and pour the concrete in the hole, mixing it with a shovel. Fill all the way to the top of the hole, or leave a few inches and backfill it with soil later to hide the concrete.
When the concrete has thickened to the point of holding each post in place, secure a fence post level around the post to level it out. Stake it so that it remains level while the concrete cures. Let the post cure overnight, then backfill with soil.
Cut the posts to the desired height with a circular saw. Remember to figure in the thickness of the cap into the height of the fence. For instance, if the height measure 5 feet, subtract an inch and cut posts to 4 feet, 11 inches.
Measure the height on the two outside posts and stretch a chalk line from these points across the others to get a line on each post. Be sure to stay level.
Set the depth on a circular saw to be half the width of a post. Score along half of the top of the post above the chalk line with the circular saw so that the cuts resemble shutters. Go back with a chisel and hammer and chip away at the scored wood pieces.
Now start attaching the 1x6 boards for rails. The top rail height should be one inch above the height of the posts, accounting for the one inch thickness of the cap. Use a level to make sure the rails are straight, then use the finish nailer and 2-inch nails to attach. Attach rails to the front and back for a double-sided fence.
Once the rails are in place, add the fence boards. Keep them about 3/4-inch off the ground so they don't attract moisture and rot, and be sure they are level with the posts on top. Nail them in with the framing nailer about 3/16 to 1/4-inch apart. You may need to use a table saw to cut down a board to fit the last space.