Final answer:
Next, Tom needs to download the placement tags, which are necessary for serving and tracking the ad on the intended media channel. The campaign and advertiser are likely already assigned since the ads and placements are created.
Step-by-step explanation:
After Tom has finished creating the ad and the placement, and has uploaded the creatives for his campaign, the next logical step would be to download placement tags. Placement tags are snippets of code that are needed to serve the ad on a website or another media channel.
These tags, typically generated by the ad server, must be implemented on the publisher's end to track impressions, clicks, and other important metrics for the campaign.
As for assigning the campaign or selecting an advertiser, these steps are part of initial campaign setup, which would generally precede the creation of ads and placements. Since Tom has already created the ads, it is reasonable to assume that the campaign and advertiser have already been assigned.