Why do you need a social network engine?

Question

Social media

Hello!
Straight to the point:
I'm making my own small social network, at the moment I have a blog and dialogs, soon there will be communities (with little functionality, but it works) :)
Then a friend advised me to use some kind of engine in order to avoid the invention of wheels.
After googling for about an hour, I could not find any accessible information about the importance of the "engine" of social networks. Everyone uses these engines - they advise others, but nowhere is there a clear answer to the question: why are they needed?
Programming has been my hobby lately, so this question may seem silly.
Please be understanding, thanks in advance for your replies :)

Answer 1

https://www.jomsocial.com
https://www.boonex.com

Answer 2

To run social networks