The want-got gap is simply the difference between what you have right now, and what you'd like to have. It's important to understand that in this sense "what you'd like to have" is limited by your perception and imagination. In some sense human beings have vast, perhaps unlimited desires (I'd like to fly through the air and visit Mars on the weekends), but in the sense intended by the want-got gap, our desires are actually quite limited, and only entail the things we actually desire to have right now and think we have a good chance of obtaining.
Much marketing is based on trying to increase the perceived want-got gap in order to motivate consumers to buy. By increasing the want-got gap between your product and the alternatives, you can increase the price at which your product will sell.
Let's consider three types of products, which should give us a good range of possibilities: Water, clothing, and cars.
Water is absolutely a need. Humans need a certain amount of water to survive, and having more than that isn't very useful to us (at least for drinking; we also use water for many other things). It is also generally fairly cheap with modern infrastructure, and in most places is of sufficient quality that people are quite satisfied with it. The want-got gap for water is quite small.
Companies such as Nestle have successfully expanded it a little bit, by pushing bottled water as somehow superior to tap water and therefore worthy of its much higher price. But even then, it's rare to find anyone who is willing to pay more than a few dollars for a bottle of water. Likewise, it would be irrational to spend a long time trying to decide what kind of water to buy, because water is pretty much water and we're dealing with small amounts of money.
Now consider clothing. Clothing is sometimes a need---many climates require clothing to keep warm, and at least in most human societies, nudity is strongly frowned upon. But clothing is really mostly a want; people don't stop at getting the bare minimum of clothing for their climate and culture, but instead purchase clothes they like or clothes that project a certain image. This creates a space for a want-got gap.
And indeed, some clothing manufacturers, such as Armani, are able to command large prices by expanding the want-got gap very wide; when consumers are convinced that their lives would be dramatically improved by this article of clothing, they are willing to pay hundreds of dollars for it even though it very likely cost only a few dollars to produce. It's also worth spending some time searching for the right clothes, because you will wear them many times or to important occasions and you may be spending noticeable sums of money.
Now we come to cars. Cars aren't really a need; people have lived without them for millennia. They could be a want, and in many cases they do significantly increase welfare. But they are probably best conceived as an opportunity: Cars allow you to do things you couldn't otherwise do. This is also consistent with the fact that cars are durable, depreciating physical capital---making them a bit like factories or robots, which are most definitely opportunities.
The want-got gap for cars is usually not very large proportionally, but cars are so expensive that in absolute terms it can be quite significant. Suppose that consumers would be willing to pay 5% more to get a better car. It's common for a car to cost over $20,000; so even a 5% increase in price is on the order of $1,000. It's well worth spending a long time researching cars before you buy them, as the differences in price and quality will have a large effect on your life.
Car companies such as Ford are also constantly adding new features, many of which most people would never even think of; this is also an effort to exploit the want-got gap. By introducing side airbags or adaptive cruise control, car companies can effectively create a desire that consumers never would have had before; maybe on some level they'd have liked to do that, but they didn't even know it was an option, so it never occurred to them to seek it out. These new features that are present on new cars but not old ones allow Ford to maintain a large want-got gap and thereby achieve higher profits.