Right column: which Customer Journey Step?
Right row: about products, content or layout?
The TPOs WPOs are organized by columns and by rows, as per the grid on the left. Each column corresponds to a customer journey step and each row to a level which is related to the type of content.
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The level 1 (the one at the bottom) is all about products (product recommendations, search results, navigation listing, ...). The level 2 (just above) is about other content / activities (banners, blog articles, vouchers, trigger mails). The level 3 is about dynamic layout (dynamic landing pages, content injection in product listing pages, PDP layout, etc.). The level 4 is for the future, it gives you an idea what we are currently working on ;)
To know what TPO WPO you need, choose the right Customer Journey step and the right level and click on the TPO WPO cell, you can then see the list of widgets in that TPO WPO and edit them or add new ones.