At it's most basic, HTML does two things – it pretties up text documents and it allows you to insert links to other documents and files. Anyone who's tried to read a ten thousand word paper presented as a hard-wrapped 40-column plain text file understands the importance of the former, while anyone who's spent any time on a system with a "mouse" or other pointing device can appreciate the novelty of the latter.
Essentially an HTML file is just a plain text file spruced up with formatting instructions contained in "tags". HTML tags are enclosed in angle-brackets and are generally placed before and after the text to be formatted like this:
<B>This tag makes bold text</B>Which will produce the following result:
This tag makes bold text
Neat, huh? Now a particularly clever individual may have already surmised that the "/" in the second tag indicates that it's the closing tag. Good job! You can go home early...
It's important that you remember to close any open tags, otherwise bad things can happen... like your whole page becoming invisible, or your entire collection of dodgy pr0n being emailed to the FBI. Really, it's just a good idea to be careful in this day and age...
Let's have another example:
<I>This is italic text...</I> but this isn't!This is italic text... but this isn't!
As you would expect, the closing tag tells the browser to stop displaying italics. Now, of course, these examples are going to be rather dull if yoiur system doesn't know how to display bold or italic text... just follow along as best you can.
So how about combining tags? This is often where good HTML goes bad. It's fairly important that tags are "nested", meaning that one tag is fully enclosed by the other. Let's have an example to clarify:
<I><B>This is bold and italic,</B> but this is just italic.</I>This is bold and italic, but this is just italic.
Now that's some fine HTML! By now you should have a basic idea of how it works... take a fifteen minute break before the next lesson.