To track sales, you need to put special sales tracking code on the final "thank you" page of the ordering process (the page which is displayed to the visitor after the purchase was completed successfully). After that, whenever this page is displayed a sale will be tracked automatically by Tracker. You can also specify additional parameters in the tracking code Ч they would be saved with every tracked sale.
Add sales manually
It is possible to add sales manually (Settings → Add a sale) and edit already tracked sales (All reports → Sales log → Edit a sale). If you will specify an ad campaign, a keyword or a split-test for a sale which you add or edit, then the sale will be attributed to that campaign/keyword/split-test and this will update corresponding numbers in the paid traffic statistics.
You don't have to specify the ID of the visitor for a sale, in that case Tracker will create a new visitor for you and will log a sale for that visitor automatically. If you will specify the visitor ID and a particular campaign for the sale then Tracker will check if the specified visitor had a click tracked from the campaign that you've specified, if it won't find any, then a click will be added automatically to the visitor path Ч this will change the numbers accordingly in the paid traffic statistics.