This feature provides keywords for different combinations of competitors that results in different suggestions. Basically you can get suggestions for keywords that your competitors are ranking quite high but you aren't and you can discover new keywords for different storefronts. You can compare the search score and the chance score of the suggested keywords for each app you have selected and see the total number of apps that are ranking for that particular keyword.
When you initially click the Keyword Suggestion tab, you see a blank page in which you'll have to select competitors to compare the keywords, then pick a country and generate the keywords. You can create a list for the apps you have selected in order to save your progress and track the keywords you see fit. The keywords you track will be added to your custom list in the Keyword Tracking module.