With drillthrough in Power BI Desktop, you can create a page in your report that focuses on a specific entity - such as a supplier, or customer, or manufacturer. With that focused report page, users can right-click on a data point in other report pages, and drillthrough to the focused page to get details that are filtered to that context.
To use drillthrough, create a report page that has visuals you'd like to see about the type of entity for which you'll provide drillthrough. For example, if you're interested in providing drillthrough for manufacturers, you might create a drillthrough page with visuals that show total sales, total units shipped, sales by category, sales by region, and so on. That way, when you drillthrough to that page, the visuals will be specific to the manufacturer you clicked on and selected to drillthrough about.
Then on that drillthrough page, in the Fields section of Visualizations pane, drag the field you want to drillthrough about into the Drillthrough filters well.
When you add a field to the Drillthrough filters well, Power BI Desktop automatically creates a back button visual. That visual becomes a button in published reports, and lets users who are consuming your report in the Power BI service easily get back to the report page from which they came (the page from which they selected to drillthrough).
Since the back button is an image, you can replace the image of that visual with any image you want, and it will still operate properly as the button to get report consumers back to their original page. To use your own image for a back button just place an image visual on the drillthrough page, then select the visual, and put the Back button slider to on. That makes your image function as a back button.
When your drillthrough page is complete, when users right-click on a data point in your report that uses the field you put into the Drillthrough filters well on your drillthrough page, a context menu appears, letting the users drillthrough to that page.
When they choose to drillthrough, the page is filtered to show information about the data point from which they right-clicked. For example, if they right-clicked on a data point about Contoso (a manufacturer), and selected to drillthough, the drillthrough page they were taken to would be filtered to Contoso.
Note: Only the field that is in the Drillthrough filters well gets passed through to the drillthrough report page. No other contextual information is passed.
And that's all there is to using drillthrough in your reports. It's a great way to get an expanded view on the entity information you select for your drillthrough filter.