Take a piece of 4x4 cedar or pine, measure and mark it to length. Remember that the base is 5/8" tall so be sure to keep this in mind as you measure the post length.
Select a piece that has no knots in the lower 6-8" of the post.
Draw two diagonal lines on post to mark the center. Or just use the 4x4 Hole Saw Center Guide that skips this tracing step entirely.
If you do not use the center guide, drill a perpendicular pilot hole into the end of the post. This will help guide the hole saw bit at the start. Be sure to have the post sitting on level ground and ensure you drill 90 degrees (perpendicular) into the end of the post. This drill has a water bubble to help guide the cut.
Use a 1-1/4" diameter hole saw to create a circular pilot cut that will assist the sharp cutting edge of the tube get started. The depth of the pilot cut is only about 1-7/8" deep maximum. The tube is 3-1/2" long so it will be driven into the wood.
Try to keep the cut as perpendicular to the post bottom as possible by sighting it from two adjacent angles.
Place the anchor tube into the hole saw guide cut and square it to the post.
Place the post anchor tube into the hole saw guide cut and push until it reaches the depth of the cut. Turn it to square with the sides of the post.
Take a look to see if you drilled your guide hole perpendicular by looking at the tube and anchor as it sits in the hole. If you really missed you can use your hole saw again. This time straighten it up.
Drive the tube into the center of the wood post with a large mallet.
Use a 3 lbs hammer, like a small sledge hammer because it has the right weight and the head is large enough to cover the whole tube.
Start tapping the tube down into fresh wood. You don't have to strike very hard. Just use gentle but accurate hits straight down over the tube until the base is flush with the post end.
If you were not quite perfect, use the mallet to strike the side of the base until it is flush. There is always enough wriggle room that you make it flush if needed.
Drill pilot holes for the four lag bolts. In soft wood you can use small drill bit 1/8" smaller than the thread diameter.
But harder woods require a pilot hole that is just smaller than the diameter of the threads or you can snap off the heads if you are not careful.
Now use a ratchet or a drill with a ratchet attachment and tighten up each lag until it is firmly inserted into the post. Use washers underneath.
So that is how you go about attaching an anchor to the post.