If you haven't already, you'll first need to add your Key Words to each Product (tutorial: see about at 3:12).
Then the fun part - sit back and let HelloProfit track your ASINs for as many as 30 Key Words, every hour! HelloProfit can only show you data since you set up the KWs for each ASIN in the HelloProfit system (not before), so over time you'll be able to select a custom date range (say for a week or a month range) and see how your KW ranking fared over that time.
If you'd like to focus just one 1 Key Word, or a group of Key Words, you can click on the Keywords themselves at the bottom of the "Search Rank By Keyword" graph, to toggle them as visible or not.
The "Search Rank By Keyword" graph is located at the bottom of the graph section on the Product Dashboard for that particular ASIN.
On the "Search Rank by Keyword Table", you can see your Key Words listed tabularly, one per row for each ASIN on it's dedicated Product Page. The "Total Results" column is the number of results on Amazon at that snapshot in time that Amazon deems to be "matches" for that Key Word. You may wish to keep that figure in mind as a relative benchmark of difficulty for ranking that Key Word. Generally the higher that number, the harder it is to rank well for that Key Word. The Page and Position columns are fairly self-explanatory, and the "Rank" column means for example if you are page 2 position 1, your rank is #15 (at least in most categories, because page 1 has the first 14 ranked products, etc.)
The Change column gives you a little indicator of whether your ranking has recently bumped up or down from it's previous position.