To upload the creative within Pexi you need a Pexi account and access to the correct advertiser. You can request a Pexi account via email@example.com. When you have access to Pexi you can upload the banner as a zip (zip the folder, not the files). If you include the IAB size within the filename Pexi will automatically detect and adjust the upload settings.
This Crossbrowser creative works as a gallery for your product. it gives you the ability to adapt the content and layout based on the viewport with as many slides as you want