What do you mean by a Campaign, an Ad-Set and an Ad?

An ad campaign defines the high-level goal and budget for your advertising efforts. It serves as a container for your ad sets and ads, allowing you to organize and manage your advertising strategy effectively.

Ad campaigns are made up of ad sets. Ad sets are groups of ads that share settings for how, when, and where to run.
Hence, a campaign is the top-most level of your ads and the ad set sits within the campaign.
Below is the summery of the campaign structure:

Campaign - You define your campaign type and main objective.
Ad set - You define who you are targeting and how are you targeting them.
Ad - Creative material (videos/images/Text) which you use in order to reach your audience / talk about your offer.

It's essential to have the right campaign structure to be profitable.