Lisa wants to know if, after viewing her Shopping ad, people are buying the shoes listed in the ad. She should:
run an Auction insights report
set up conversion tracking
use enhanced cost-per-click (ECPC) bidding
run an Ad performance report
Conversion tracking is a free tool that shows you what happens after a customer clicks on your ads — whether they purchased a product, signed up for your newsletter, called your business, or downloaded your app. When a customer completes an action that you’ve defined as valuable, these customer actions are called conversions.
Read more here: https://support.google.com/adwords/answer/1722022