JavaScript importing module confusion

When I am importing ‘http’ module, I use

Var http = require('http');
http.createServer(function(req,res){......
}.listen(8080)

But when I am importing express module, I use

const express = require('express');
const app = express();
app.get('/', (req,res)=>{........
}
app.listen()

Why do I need to create const app = express(); but not const app = http(); in the code?