document.getElementById("idName")

//This method only returns the one element by the specified ID. 

document.getElementByClass("className")
//This method returns all elements inside the whole document by the class you specified.

document.getElementById("someElement").getElementsByClassName("className")
//It works in all elements of the DOM, this will return all elements by the class you specify inside the element you want

document.querySelector("#idName")

//This method takes one argument, which is a CSS selector & returns the first element that matches the selector. 

document.querySelectorAll(".className")

//Works similar to above; returns a node list collection of all matching elements.

document.createElement("body")
//this method creats the element, but it does not show up on the page.

document.body.append(element)
//this method gets the element to appear on the page.

<h1 id="greetings"> HELLO </h1>

let element = document.querySelector("#greeting")
element.innerHTML = "Welcome"
//selects the h1 called greetings and changes HELLO to welcome

const element = document.querySelector(".container")

element.style.backgroundColor="#f0f0f0"
//changes the selected elements(in this case the container class) color to grey

element.remove()
//removes a whole element from the page