Impression statistics can help you evaluate how effective your banners are. After impressions begin, you can view reports on the performance of the ad campaign in the Report Wizard.
For example, you can see the search queries that triggered your ads. Under Sections, choose Banner number and Search query, and under Columns, choose Clicks and Bounces. To prevent Yandex.Direct from serving ads for non-relevant searches, use negative keywords. You can add them on the page where you edit your campaign or banner group.
Read more information about campaign statistics.