How does the server know the request HTTP verb

Express abstracts those things away, but whenever you make a request to the server, a lot of data is sent, along with that data is a header, which contains information like the type of request ('PUT', 'GET', etc..).

By default, a request is a 'GET' request, but when you make an interactive element on a website (usually a form or a button) you can specify the type of request being sent.

A form is often a 'POST' request for example (but not always).

I believe this course gives a bit more insight into it.

On the client side, we include the type of request that's happening in our code. Let's show a simple XMLHttp get request:

const xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
       // Typical action to be performed when the document is ready:
       document.getElementById("demo").innerHTML = xhr.responseText;
    }
};
xhr.open("GET", "filename", true);
xhr.send();

You can see here that in our request, we explicitly state that it's a "GET" request. We could change that value to post and include our json info. Or if you're more used to fetch:

fetch('https://example.com/profile', {
  method: 'POST', // or 'PUT'
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify(data),
})
.then(response => response.json())
.then(data => {
  console.log('Success:', data);
})
.catch((error) => {
  console.error('Error:', error);
});

This way, we let the server know what kind of request we are making.

https://en.wikipedia.org/wiki/Internet_protocol_suite check this out.