Once you have signed up for retargeting, the next step will be to create your own display ads for the retargeting campaign. This is done very similar to setting up a normal marketing piece, and the first step is the same.
Head to your Marketing Materials page, then click Create New Marketing piece. You can have multiple ads running at the same time, but for now choose the display ad template you'd like to get started with.
Proceed through the steps, and find yourself on the step where you can drag over a listing into the piece. Proceed another step and you can edit how that image displays.
With the sliding bars, you can edit the vertical position, horizontal position, as well as overall size. This might take a bit of playing around with until it looks nice.
Once you've got it looking as you'd like, proceed to the final step to submit the ad for approval. Generally this takes 48 hours, after which time this display ad will be up and running!
Repeat for the other size of ads you'd like to use. At the end, you should have all three sizes submitted: