File Server
All servers come down to being basically file servers, and it is one of the
easiest to get started with as all operating systems come with the ability to
share files across the network, the origins and date back to the building blocks
of the Internet, where there was a need to distribute files and data between two
machines.

Since then a lot has changed, and while file serving is easy, a little thought
about security and file availability needs to be made to protect data.
Hardware
A running home server is already a file server, so there is not much extra
requirements to start serving files. Hard drive capacity is favoured over speed
for realistic use in the home, SSDs are touted as speeding up a computers
performance. But on a modern operating system hundreds of system file can be in
use at the same time, here speed can improve performance however network shares
only utilise a handful of files at a time.
Having higher capacity drives gives the opportunity to bring all your files from
different systems to a central source, and as servers are meant to run 24/7 they
will always be available. When files are central it's important to look at
protecting the data from a security and failure point of view.
Mechanical hard drives are the most likely component to fail first on a computer
system, leading to lost data and a world of hurt if that data was important, to
give protection against failures one can either have backup or redundancy.