The event loop.
The event loop is a powerful tool/feature of node.js, as well as any browser, that can be manipulated to help build a very powerful product, but what exactly is it? Where does it lie? How do you know if you are exactly using it? Well if you think of the event loop as either a server at a restaurant or a car in a nascar race, you will be able to get a bit of a handle on the concept.
So the understanding the power of the event loop comes first in understanding the difference between synchronous and asynchronous actions. A synchronous action is when a list of events happen one after another, while an asynchronous action is when a list events happen but there is nothing determining when which event will finish first. So imagine a server a restaurant that had two tables. The server takes the first tables order then waits in the kitchen until the food comes out, serves the first table, then goes to the second. That would be a synchronous approach which, while if the server took both tables orders and then gave out orders to respective tables as the food comes out, regardless of who order comes out first, would be an asynchronous approach. Separating your concerns will help you figure out when and where which action is preferred.

With separating your concerns, you would also want to have a plan of attack when utilizing the event loop. So I am about to make a nascar analogy so bare with me. With nascar, each race is planned out from beginning up until the very end. Placement, the track, weather condition and many other factors are all taken into account when creating the plan for a successful race. As the race starts, you then have a plan for when your car is going to come in for a pit stop and what type of pit stop each visit will be. The same planning will be needed when working with the event loop. You have to have a plan for how many actions will be taken place and how you will serve them and when they need to be served to your client. Keep in mind, just like in nascar, just because an action started first does not mean that i will finish first.

The event loop in node.js accepts many different asynchronous actions at a time while simultaneously placing them back into the single thread that javascript executes its code on. Combining both our server and nascar analogies, having a plan based off of when an action needs to execute and when they need to be served is a great way to utilize the power of Node.js
