Last week, you saw a page with one long paragraph of text. But as you can see, I can now divide my text into paragraphs.
You should always use the HTML headings in numerical order. Yes, H1 is really large when it's unstyled, but it is the top-level heading, so should be used first - usually as the title of your page. Once you have an H1, add the other heading tags below it.
If you want your text to be strongly emphasized or just emphasized, use the strong and emphasis tags.
As always, check out the source of this page to see how I did what I did.
Have fun, and congratulations on writing your first Web page.