In order for the statistic to be logged, the Web analytics module must be enabled in Site Manager -> Settings -> On-line marketing -> Web analytics.
Once some hits are logged by this web part, the reports that will display the statistic's data can be created in CMS Desk -> Tools -> Reporting. The results can then be viewed in the CMS Desk -> Tools -> Web analytics interface under the Custom category.
Detailed information about creating custom statistics and their reports may be found in the Web analytics chapter of the Kentico CMS Developer's Guide.
Help URL: http://devnet.kentico.com/docs/webparts/index.html?AnalyticsCustomStatistics_overview.htm