Before you can understand how to program the web, you need to understand the web itself on a more granular level than you probably do now. Some of this stuff is necessary just to have a more wholistic understanding of the ecosystem in which you will be working (and to not sound like a total newbie when talking to other developers about it), but other aspects (like HTTP) will come up again and again when you start programming.
We'll also cover a few tips and tools that will be useful to you again and again going forward.
For a basic and painless Internet overview, check out Don't Fear The Internet's Simple Primer (video):
For a basic explanation of how packets work, check out this video called How Does the Internet Work?:
Harvard's David Malan explains internet basics in this lecture (start at 52:15) from his popular Intro to Computer Programming course. Note the "developer tools" section of the browser that he talks about around minute 58... you'll use that a lot. We'll get heavily into HTML later in the curriculum.
David dives further into HTTP in a short 3-minute video (video)
You've heard of your browser's Developer Tools tray but probably don't fully appreciate yet exactly how useful it is.
Check out some more on the developer tools from Don't Fear the Internet:
To learn more tricks about how to use your developer tools, check out this video:
Are we moving too fast? Stop, settle into your favorite chair and pull up What is Code?, the incredibly accessible and thorough explanation that Paul Ford provided his Bloomberg editor when asked the same question.
This section contains helpful links to other content. It isn't required, so consider it supplemental for if you need to dive deeper into something