Library Or Framework Programming Guide

Alright, let's set up a basic REST API using Node.js and Express. We'll stick to the MVC architecture and handle GET and POST requests. I'll also explain middleware as we go through the steps. Here's a step-by-step guide:

Install the necessary modules: 
You need to have Node.js installed on your computer. After that, initialize a new Node.js project by running npm init -y in your project directory. This will create a package.json file for your project. Next, install Express and other necessary modules using npm:

npm install express body-parser

body-parser is a middleware used to extract the entire body portion of an incoming request and expose it on req.body.

Setting up your server: 
Create a new file named app.js (or server.js), this will serve as the entry point to your application. Here's how you can set up a basic server:

const express = require('express');
const bodyParser = require('body-parser');

const app = express();

// Middleware for parsing bodies from URL
app.use(bodyParser.urlencoded({ extended: true }));
app.use(bodyParser.json());

app.listen(3000, () => {
  console.log('Server is listening on port 3000');
});


Setting up routes (Controller in MVC): 
Let's create a new directory named routes and a file within it called api.js. This file will contain our routes.

const express = require('express');
const router = express.Router();

// GET request
router.get('/items', (req, res) => {
  // handle the request
  res.send({ type: 'GET' });
});

// POST request
router.post('/items', (req, res) => {
  // handle the request
  res.send({ type: 'POST' });
});

module.exports = router;


Use your routes in the application: 
Now, we need to use these routes in our application. Add this in your app.js file.

const apiRoutes = require('./routes/api');
app.use('/api', apiRoutes);

Now your application is setup to handle basic GET and POST requests.
Middleware in Express is a function that has access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. The next middleware function is commonly denoted by a variable named next. 
Middleware functions can perform the following tasks:

Execute any code.
Make changes to the request and the response objects.
End the request-response cycle.
Call the next middleware function in the stack.

In our setup, body-parser is a middleware that handles the parsing of request bodies.
Keep exploring and expanding your API from here. You may want to connect to a database next, for which you might use another library like mongoose for MongoDB. Enjoy your journey in Express and Node.js!