It’s mostly about how people spend their money, that is to say: who buys, how they buy and what the selection criteria are. 


Who buys? And more importantly, who is important in the buying decision? That’s not always the same, the person making the purchase is often different from the person who will use the product. Both may be different from the person with the power and the financial authority to make the ultimate choice of the product purchase (parents?). And of course, there may be some other persons influencing the outcome of the decision or even trying to impose their choice criteria on the decision. As you see, there may be many actors that you would need to convince that your solution is the right one.
How do they buy? The way organisations buy things is radically different from the way users (as individuals) purchase. Allow me to focus on consumers. It generally starts with the identification of a need  or a problem. Then the user will do some information search and try to find a solution. They might of course come across many solutions that they would evaluate and select the one they judge as best. 
But how do they know, which one is the best? What are the choice criteria? Well, the criteria are various:
Technical criteria are related to the performance of the product or service (reliability, durability, performance, convenience, etc.)
Economic criteria concern the cost aspects of purchase (price, running costs, value for money, etc.)
Social criteria concern the impact that the purchase makes on the person’s perceived relationships with others, and the influence of social norms on the person. 
Personal criteria concern how the product relates to the individual psychologically, given that emotions are an important part of decision-making for the customer (for example, some prefer a product just for love for a brand).
Wow, that’s quite a lot of information to process, isn’t it? Wait, to process it, you need to have that information in the first place. Before even understanding what they want, you need to know what they want, so you need to know your users, how do you do that? Through some more or less advanced research, hence the next point : Research and Information systems.