HTML document greyed out

I am loading my first document into Sigil.

When I tried to open a file, it was greyed out and wouldn't open.

So then I "add file" and that worked, but my view is full of code. That's okay I can handle lots of code, but I wonder why I couldn't open a html file and if adding it instead messed up the format somehow.

I have some screen shots here. https://monacurtis.com/images