Computer people will often talk about a ‘server computer’ and it can sound like they are talking about a computer that is somehow different from a desktop computer (or a laptop or a tablet or a phone).
But a server is any computer (or device) that provides services to other computers (or devices). So if – for instance – you share photos with another computer in your house or office then the device doing the sharing is a ‘photo server’. It is the act of sharing that turns the device into a server and not the technical specification of the device.
There is no need for small businesses to buy very highly specified so-called ‘servers’. A standard refurbished computer (for example: with Windows installed but other operating systems are available) can share files and email in a small business environment (for example: an office with ten computers) and there will be no problems.