Okay kiddo, imagine you really, really want some ice cream. You keep asking your mom or dad to buy it for you, right? This is you creating "demand" for ice cream.
Demand is when people want or need something, and are willing to pay for it. It could be ice cream, or toys, or clothes, or anything, really.
But it's not just about wanting something - there are also other factors that affect demand. For example, if it's really hot outside, more people might want ice cream, so demand for it would go up. If lots of people are suddenly interested in a certain toy, demand for that toy would also go up.
But on the other hand, if something becomes too expensive, or if people can get something else that's just as good for cheaper, demand might go down. So there are lots of things that can influence demand.
And why is demand important? Well, the more people want something, the more likely it is that companies will make and sell that thing. This means that companies will try to attract as much demand as possible, by making things that people really want and making them at a good price. So ultimately, demand helps us get the things we want, and keeps the economy going!