Difference between sessions and cookies in Express

//app.js

const express = require("express");
const cookieParser = require("cookie-parser");
const app = express();

// Middleware to parse cookies from the request
app.use(cookieParser());

//Route to set the cookie
app.get("/setCookie", (req, res) => {
    // Setting a cookie
    res.cookie("username", "GeeksForGeeks");
    res.send("Cookies set successfully!");
});

//Route to retrieve the cookie
app.get("/getCookie", (req, res) => {
    //Retrieving cookies from the request
    const username = req.cookies.username;
    res.send(`Username: ${username}`);
});

//Route to delete the cookie
app.get("/clearCookie", (req, res) => {
    // deleting a cookie
    res.clearCookie("username");
    res.send("Cookie deleted successfully!");
});

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

//app.js

const express = require('express');
const session = require('express-session');
const app = express();

// Middleware to enable sessions
app.use(session({
    secret: 'secret_key',
    resave: false,
    saveUninitialized: true,
}));

//Route to set the session
app.get('/setSession', (req, res) => {
    // Setting session data
    req.session.username = 'GeeksForGeeks';
    res.send('Session set successfully!');
});

//Route to retrieve the session
app.get('/getSession', (req, res) => {
    // Retrieving session data
    const username = req.session.username;
    res.send(`Username from session: ${username}`);
});

//Route to destroy the session
app.get('/destroySession', (req, res) => {
    // Destroying the session
    req.session.destroy((err) => {
        if (err) {
            console.error(err);
        } else {
            res.send('Session destroyed successfully!');
        }
    });
});

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