General
9 Step Tutor
How to Create Your htdocs folder
This information is older than methuselah and I haven't used windows in over 10 years, so take it for what it's worth.
This procedure would have worked on most Windows platform computers.
Just follow the steps using the screen shots shown below:
Click Start button bottom left of your Desk Top, then Computer

Locate your C:/ drive and double click on it.

Find an open space in the right pane and right click or on newer versions of Windows, Click the drop down arrow beside Organize top left, and choose New Folder.

If you Right Clicked, Click New then Folder

Either method, Type htdocs to replace the blue New Folder text.
Then click beside it.

Then double click the htdocs folder to open it.

Right click on a blank space inside the folder and choose New then Folder or use the Organize button again.

Replace the New Folder text with the word images.

Now when you save firstpage.html in the c:/htdocs folder, you'll be able to type file:///c:/htdocs/firstpage.html into the top of your browser and preview the web page.
When you save your images in Exercise 6 you'll save them in your c:/htdocs/images folder.
Linux Users
The Firefox/Linux browser has a security setting somewhere that only allows it to see about 4 folders when using it offline. Even the techs can't provide a solution to their own tool.
I wanted to be able to test with Firefox so the only solution I could come up with was to move the htdocs folder into a folder it sees.
My htdocs folder lives in my Downloads folder.
The best browser I've found for working offline is the Microsoft Edge/Linux tool.