for the OP, servers can usually be accessed by other people on the network. For example, I have a Synology NAS (Network Associated Storage) that is connected to my router. My music systems are in other rooms, each one having a streamer that is connected to the network by Ethernet, but wifi could be substituted. The streamer takes music from the NAS and sends it to the audio equipment in whatever system is being played
At the same time that I access the NAS for music files, my wife can download or upload photos on the NAS. Potentially movies can be be stored on a server and watched while music is being accessed.
Hopefully this helps understand some of the terminology