A server is a computer, and you can do everything with it that you would with your home or office computer, for example, store files and install software. The only difference is that the server works continuously, that is, it is connected to the Internet and to the power supply 24/7. Work with such a computer is carried out remotely, according to the server-client principle, where your personal device acts as a client. Thus, the server's files and programs can be accessed at any time.
Before buying a server, namely buying it as a physical computer, you need to understand that to ensure its operation, special conditions are required, the organization of which requires a lot of investment. For large companies, this may be a necessity. However, server rent is most often in demand. Thus, you can buy a server from a hosting provider and pay a certain tariff.
Hosting providers organize special premises — data centers, where the server and server equipment work, they also provide all the necessary resources and technical support for smooth operation.
A server is not necessarily a super powerful computer, its main qualities are reliability and fault tolerance. Therefore, the server is chosen for the specific tasks that it will perform. Specific task servers can be:

1. Web server. Web servers store all the material that makes up web sites. The site visitor sends requests through the browser of a mobile device or a personal computer playing the role of a client. The web server responds to the request in HTTP format by sending data to the client, and, as a result, the site is displayed to the visitor on the screen. Thus, the visitor can navigate through the pages and interact with the Internet resource.
2. Game server. Game servers provide interaction between players in the virtual world of one game online. Examples include World of Tanks, World of Warcraft, DotA and Counter Strike.
3. Video server. Video servers are used to store video content. With the help of this server, the user gets the opportunity to watch video from his device without downloading it. An example of a video server is YouTube.
4. Mail server. Examples include Gmail, Mail, and Yandex. Email servers store e-mail, they are used for forwarding letters, sorting emails, filtering spam, etc.

There are many other servers such as local network server, FTP server, VPN server, DNS server, Proxy server. Different servers are designed for different computing power and volumes. Therefore, if you want to buy a server cheaply, then choose its parameters based on your needs, so you will not overpay for unnecessary resources and functionality.