Morgan is used for logging request details. However, the snippet in your question doesn’t make sense because it’s not actually a single coherent snippet top to bottom. It is a series of examples of the various types of options you can pass to morgan. In a real program, you would only need one of them. For example:
var express = require('express')
var morgan = require('morgan')
var app = express()
//This tells express to log via morgan
//and morgan to log in the "combined" pre-defined format
app.use(morgan('combined'))
//That's it. Everything in your snippet after this are just
//other variations your might want to use