The anatomy of a PPC campaign can be hard to understand for beginners starting out in paid search. In my opinion, it's easier to understand the anatomy of a paid search structure using visuals!
The highest top-level layer is the account-level layer. On the account level, administrative settings can be set such as: account alert preferences, auto-tagging, billing information, and account access permission.
Within an account, you have a layer that contains entities called 'campaigns'. You can create up to 10,000 campaigns within 1 account.
Each campaign has configurable settings that define when and where your ads appear and to who.
Network - a network is where your ad will appear. In general, you have two options: on a website or on search results pages. If you want your ads to appear on search results pages, you want to target the 'Search Network'. If you want your ads to appear on websites, you want to target the "Display Network".
Device - you can specify whether or not you want your ads to show up on Desktops and Laptops, Mobile devices with full internet browsers, and tablets.
Location - specify where you want your ads to show geographical-wise.
Budgets - specify how much you want to pay per day for each campaign in your account.
Bidding - several bidding options exist such as automatic bidding, CPA bidding, CPM bidding, CPC bidding.
Language - choose from many different languages.
Campaign Negatives - although technically assigned on the keyword-level, campaign-level negative keywords exist on the campaign level.
Ad Extensions - extend your ads with sitelinks, location extensions, product extensions, phone extensions and several others to stand out amongst the crowd.
Another way to think of a campaign is as a container that holds 'ad groups'.
Ad Group Level
Ad groups are the third hierarchical layer within a PPC account. Ad groups exist within campaigns. To put this in perspective, 1 account can have up to 10,000 campaigns. Within EACH campaign, you can have up to 20,000 Ad Groups. So what are Ad Groups? Ad groups hold keywords and ads.
Keyword and Ad Level
Keywords and ads belong to ad groups. On the keyword level, you create specific keywords and ads and put them into specific ad group. The overall idea is to group similar keywords together (an ad group) and to write specific ads related to the group's specific theme.
Check out Google's explanation on the Anatomy of a PPC campaign for more info!