For example, if you have four banner promotions included in your newsletter, the banner ranked #4 with appear in the highest placement in the newsletter while the banner ranked #1 will appear in the lowest (closer toward the footer). If you have square promotions, the square ranked #4 will appear first on the left side and the square ranked #3 will appear on the right side and so on.
For Lead Posts, the highest ranking will go into the most featured spot. Keep in mind that for some templates, the colored or highlighted box towards the middle is considered the most featured spot so the highest ranked post will appear there. For example, if you enter three Lead Posts, the post ranked #3 will go into the highlighted box, the post ranked #2 will go into the first "regular" post slot and the post ranked #1 will follow after that. If your template does not have a highlighted box and has the featured spot as a larger article at the top, the articles will appear in the normal highest to lowest numerical order.