Many people find it useful to write their introduction after they have written their assignment. They find that it is through the process of writing their assignment that they clarify the overall point they wish to make in addressing the set topic. They then draft their introduction at the end, or they return to their initial attempt and re-write it. Refer to What does a good conclusion look like? for an example of this. Of course, some people prefer to start with an introduction that helps guide their writing. Either way, it is still good practice to ensure your introduction says what you want it to say!
If you use your web browser's view source feature (see the View or File menus) you can see the structure of HTML pages. The document generally starts with a declaration of which version of HTML has been used, and is then followed by an <html> tag followed by <head> and at the very end by </html>. The <html> ... </html> acts like a container for the document. The <head> ... </head> contains the title, and information on style sheets and scripts, while the <body> ... </body> contains the markup with the visible content. Here is a template you can copy and paste into your text editor for creating your own pages: