Each company page post gives you metrics to help you determine which post does best. "Clicks" refer to the number of people who click on your post, either to view the content or to come to your company page. "Impressions" refer to the number of eyeballs on your company page post, either in their news-feed or on your company page. One person can account for more than one impression. "Engagement" is the collective number of likes, comments, shares, and clicks, divided by impressions -- it's given to you as an engagement rate. This shows you if you post was engaging to your followers.