I need help completing the challenge tasks, the contact.html page is unavailable.

If I remember correctly, you have to create the two files. Try right-clicking on the left panel and see if a 'New file' option appears. From there you can save the file as 'contact.html' and 'about.html'.

Was this not explained in the video?

My workspace is working well. It in completing the 'Challenge Task', I seem to be unable to flip between the files. I could in earlier challenges. sigh....

Just so I understand what you're asking correctly.

You are having difficult 'Adding' both a contact.html and an about.html file to your workspaces?

And/or once you have files added to your directory (appearing in the dark grey panel on the left of your workspace), you are then having trouble switching between them in the workspace browser?

yes. you understand correctly. amazing.... This is with the challenge only though.
I am thinking that I on the challenge, I should be able to write code on just the challenge sheet (this is integrated with the videos and is separate from the Workspace. In the Challenge section, there isn't a dark grey panel on the left side. I am assuming one can write code just on the 'one sheet' (its a dark screen to type in lieu of the video screen) I hope this is clear.

Separate issue: I am noticing the web page (which is being developed in tandem with the work space-white screen with grey panel on left) does not adjust for margins on the right. Objects and text scroll off the viewport screen, and are partially concealed.

Where would I begin to look for this "margin on the right side of screen" issue?

Thank you.