As you can see, the structure of a campaign is very simple.
Campaign : you have to put the product or the service that you provide to customers. The advantage of segmentation of your campaign is to analyze separately performances of each campaign for each “family of product”. This picture show you two types of furniture but we can imagine to add Garden furniture or kitchen furniture.
Ad Group : it’s represents the subcategory of the campaign. You have to accurate more details about products or services. Add the different type of products of the range. the proper term is the width of the range. As you can see for Campaign “Tables” there is 2 products, “Coffee Tables” and “Bedside Tables”. If you have more models of tables, create an other AdGroup.
Ads : Your ads appears on the Google Display Network on the right side and also above organic research. this could be your ads that display on this page, take example of well-known companies to create your ads if you have difficulties. The position of your ads depends of quality score that google give you. It’s a rank between 1 and 10, more your quality score is high, less you will pay for your ads. Look at the lesson about quality score to learn more about it. 
You learn more and more… You are just annoying. Next time, it will be you who will give me the lesson… 😛
Related articles
- Improving AdWords Quality Score Reporting (adwords.blogspot.com)
- Lesser Known AdWords Quality Score Facts (seroundtable.com)
- What The Heck Is AdWords Quality Score And Why Does It Matter Anyway? (searchengineland.com)
AdWords Lessons 