A server is a running instance of an application (Software) capable of accepting requests from the client and giving responses accordingly.
A Server is a Takeout Restaurant
When you're at home and you want some chicken wings, you might order take out. This is a lot like using the internet. You want something specific that a restaurant offers. You know how to request it. So, the restaurant can provide it. They have the equipment, staff, food, and recipes to serve up the stuff you want. You don't have to know anything about that though. You just ask for chicken wings and they take care of it. Once you place your order, they prepare the meal and send it back to you via a delivery driver.
A server on the internet is very much the same. The server is a computer that has the ability to provide something you want. This could be a video, an image, your Facebook profile, or the latest news. You don't have direct access to the server, but you know how to talk to it using your web browser. The server has all the special hardware and software to serve you what you want. Once it has the response you need, it sends it back to your computer via the network connection.jacksongabbard