What you need to know
How they work?
A server is running an application cabable of accepting requests from the client. A client is a piece of hardware or software that access services made by the server. A server can be run from any computer, including a dedicated one. The sever preforms task from the request of the client.
Where are they used?
Servers can be used in offices, organizations or any place where they need to store large amounts of data. You can store your data in the server and at a later date, you can retrieve it. This will leave your own computer with much more space.
Another example of this is a gaming server. It runs the application and then use a client to access this. This allows multiple people to play at once. Minecraft is an example of a game that allows users to play together.