What is networking?
Networking connects machines, services, and users.
What it is
Networking is the network around the app. It decides which machines can see each other, which ports they use, and how a request from outside reaches the right service. Without those connections the code only runs on the machine where you started it.
The process can be running and still be unreachable if it sits on the wrong network or the port is closed.
What it is made of
A service listens on a port. The web server usually uses 443 for HTTPS, a database often stays internal, with no path in from the internet. Between them are network areas: the public network, a private network between your servers, and sometimes a separate network only for the database. A request takes a concrete path. If the service sits in the wrong network, or the port is closed, the request does not arrive, even when the process is running.
What goes wrong
You decide who may talk to whom. The app may reach the database. The internet may reach the app. The database should not see the internet directly. That sounds like a one-time setup, and it comes back for every new server, every new environment, and every new project.
What you otherwise look after yourself
If the network is wrong, you see timeouts, connection errors, or a service that works locally and not from outside. Often the code is fine and the path to it is not.
How it shows up on MainPath
MainPath creates the server and reachability with the project, so services can reach each other and users can reach the app. More on that is under Servers.