The client-server model operates kind of like a microbrewery.
In this microbrewery, your goal is to sell a high volume of beer to bars, liquor stores and supermarkets. You have a variety of customers that will make large orders every week or every month.
This means that customers will call your sales team or send an email every so often with a request. On the internet, this is known as a client.
On the other side of the equation, your brewery operations team exists so that it can brew beer that will meet the demands of the customers. In this situation, they are the server. That means that they await requests from clients, and use their computing power to share the appropriate resources based on the request.
In a very basic example, a supermarket might send a request like “We need 20 cases of beer.” At some point in the future, your microbrewery will send the response: the beer that was requested.