Sessions will only appear in the sources report if the tracking URL has been viewed at least once during the time frame of the current view. Click on the dropdown at the top of the sources report to change the time frame.
Make sure that the HubSpot tracking code is installed on the page that the tracking URL is linking to. Tracking URLs will not record page views for pages without the tracking code, such as pages external from your website, PDFs, images, and documents.
Insert your HubSpot full tracking URL into the Final destination field in AdWords ads, not the Destination field.
The Final destination field will need to contain the same domain as the landing page URL. For example, if your ad's landing page is http://offers.yoursite.com/demo your Final destination field will need to contain yoursite.com.