You have electrical power supplied to your home. It is literally an electrical current, a flow of electricity through those wires. When you need some electricity, to charge your phone, for example, what do you do?
You simply take your charger and plug it into the socket that is connected to the current.
The relationship between the charger and the electrical current is in some ways similar to that between plugins and WordPress. From the start to the final page display, a whole sequence of events happen. It is like a flow from the user’s request to the page display. Not very different from the flow of electricity.
A request from the browser is Point A and the page rendered is Point B.
At different points on this flow are sockets that we can plug into. Between points A and B, there are a lot of steps working in a particular way. At times, we need them to work in a different way. At almost each such step, is a socket for us to plug into.
There are different types of sockets and different ways of plugging in WordPress. And that’s the subject of another post.