At this step, you will be creating your campaigns and ad sets. You may start from scratch by selecting Create New Campaign or you may load an existing campaign.
You may use Campaign Budget Optimization which is a way of optimizing the distribution of a campaign budget across your campaign's ad sets. This means Facebook automatically and continuously finds the best available opportunities for results across your ad sets and distributes your campaign budget in real time to get those results. Read more about CBO here.
Existing ad sets can also be used. You may browse existing campaigns, and ad sets, sort them by impressions, date, name, date created, and status.