The Dimensions tab in AdWords allows you to view performance metrics segmented by dimension across account, campaign, or ad group levels. Key dimensions include time (day, week, month, etc.), conversions (conversion types), geographic location, and search terms. Reach and frequency metrics show the number of unique users exposed to an ad and the average number of exposures. Other dimensions include destination URLs, demographics, automatic placements, and call details. The free clicks report measures pre-click interactions like expanding product info or hovering over display ads.