You've asked a very large question. But I'll give it a shot.

Html and css are the building blocks of Web pages. Css is the style of the page like colors, spacing, etc. Html is the structure.

A server serves up an html page to a user when the user requests it. The user can then modify info a send something back to the server. The server does stuff with that info and sends a new page back. This repeats over and over till you leave the site.

A domain name is basically an address for the server. There is some complicated mapping that occurs through a DNS that translates the ip address of the server (numbers like 127.0.0.1) to words that we can recognize and remember easier.

The difference between what google does and a high school kid is drastic. The scale at which google operates is just not possible for an individual. But basically google has to maintain a lot of equipment and data structures while maintaining security, usability, and am overall enjoyable experience.

The real bread and butter of what google does is how fast they can send those pages back and forth. Take google docs for example. As two people type the letters show up instantly. There is soooo much going on there that I can't explain in this alone. But basically google maintains such a high quality product that takes hundreds of people to maintain. A lone developer can do cool stuff like Google docs. But most projects quickly require a team of people to work on to make deadlines.

I have simplified this for brevity. There are dozens of Web languages, different kinds of servers, front end apps, back end api interfaces and all that takes years to learn. And decades to master. Which is why those who have no idea how basic tech things work don't bother to learn it.