Between the posts using the mounting screws set to the six pre-bored holes. For extended fence-lines, this procedure is covered in depth in the PDF Installation Guide, found on the Regarding Installation page. This also accompanies all shipments as a paper copy. Basically, string a line along the fence-line, set the two end posts, and work your way down, setting a post, mounting a panel, setting a post, mounting a panel, etc. The posts are set, at this juncture, in pea gravel, allowing for final adjustment before setting them to a 6″ cap of concrete.
This is also covered, with pictures, on the Example Fence Layout page.
*As a note, there are those installations where the installer prefers to set the posts first, and take measurements once the posts are set. This is fine, as long as the measurements between the posts are the same. e.g. if you have a length of 10 panels called out at 59″ net width and the pre-set posts are set such that we have some at 59″ and some at 58-⅞”, etc, then we can no longer gang-cut  the rails all to the same length. So if the posts are to be set prior to the panels arrival, be sure to use spreaders to insure the distance between each post is exactly the same.