So There are many sort of browsers
FireFox, Chrome, Opera and etc.... These web browsers interprets the files from server to the website we use to see
Usually, websites consist of 3 files
HTML, CSS and JS
Why are there different types of files?
They have different jobs.
HTML Code file is responsible for the structure of your website.
If a website was a house, HTML's role is to build a wall or floor or pillars. They are basically the structure of a house.
You can make the structure of a website and add a button or add a text box and many things related to the structure.
CSS code file is responsible for styling your website.
If a website was a house, CSS's role is to paint a wall or measure the height and width of the objects in a house or etc.. You can make the house look the way you want it to.
You can change the font and also color of the background of your website. These things are done by CSS
JavaScript code file is reponsible for behavior of your website
If a website was a house, You would have to connect the wires to the plug so that Your light bulbs switch on.
Js allows your website to have behavior
In conclusion, These 3 files are integrated and show you a website you always or use to see.