Campaign, Ad Group, Ad

Every X campaign is built in three nested levels: the campaign holds the objective and budget, ad groups hold the targeting and bid, and ads are the posts people actually see.

You set the objective and total budget at the campaign level. Under it you create one or more ad groups, and each ad group carries its own audience, placement, schedule, and bid. Inside each ad group you attach the ads. Change the audience and you are editing the ad group, not the campaign.

Say one campaign has two ad groups: one targets keyword searches, the other targets people who look like your followers. Same budget pool, same objective, but Ads Manager shows the keyword group returning results at half the cost. You shift weight by raising the bid on the group that works, not by touching the campaign.

Budget lives at the campaign level, targeting lives at the ad group level. People try to give one audience its own budget, cannot find the setting, and give up, because they are looking at the wrong level.

Objective up top, audience in the middle, creative at the bottom. Always.