Install the Posts
Use a post-hole digger or a utility loader with an auger attachment to dig holes for the posts. Slip the posts into the holes, level and plumb the posts and backfill with quick-drying concrete.
Even up the posts. Once the concrete has dried and the posts are secure, check the tops of the posts to make sure they are level and trim off one post with a reciprocating saw if needed.
Safety Alert: Reciprocating saws can have a powerful kick that can make them difficult to control. Use a hand saw or have a helper trim the posts if you are not confident. Be especially careful when working atop a ladder.