Turn on the Lookalike section with the Enable Lookalikes button. In the Source Audiences field, search for and add one or more existing custom audiences from the account. Each source you add becomes a tag, and you can combine several. Then select the percentages you want (1%, 2%, 3%, 5% and 10%) and choose the Country (the default is Brazil). Ads Editor creates one lookalike for each combination of source and percentage. For example, 2 sources with 1% and 3% selected create 4 audiences. Names follow the pattern Lookalike - SourceName - 1%. Important: retention periods don't apply to lookalikes, so you don't need to select days to create them.