I'm still learning Inkscape and am very much a a beginner. To the best of my recollection, I did not go poking around in settings or anywhere else that may have caused my problem. But obviously I've done something to cause this issue as I'm sure it's operator error 😥

If I draw a line, I see nothing.

I I give the line a stroke color, nothing happens.

Lines aren't supposed to have any fill, right? But that's the only way I can see the line.

If I use the shape tool and draw a circle, it will fill with red, but if I choose say any other color for the stroke, it won't show up, and of course if I remove the circle's fill color, the circle just becomes invisible.

Line width is 10mm. My document is A4 and in size mm.

What have I done? 😥 I feel like I broke Inkscape. I have got to get things working properly again.

Please offer any help you can. Thank you.

Even going back into the tutorial, my rectangles are not defaulting to having a black outline. I thought I just corrected the settings for that, but it seems like I did not

sigh, calligrahy tool works, and if I switch to pencil tool I can see my lines. However, I use the pencil tool and just click once anywhere, drag to make line, click to end line, I see an invisble line :(

Take a look at the Fill & Stroke panel on the right in the first screenshot you posted. Look for the horizontal colour band labelled 'A'. See how it's at zero? That means it's full transparent. Drag it up to 100 and you'll see your stroke. 'A' stands for Alpha which basically means transparency.

Thank you z3z. I appreciate your time and advice. I am exhausted (my fault from completely overreacting to my Inkscape issues). I promise I will try this later this evening or first thing tomorrow morning. For now I need a bit of a break from the computer. I will report back to let you know how things went.

Hey z3z. Sadly, I'm still not seeing the stroke.

I understand the concept of fill and stroke but actually using the interface (fill and stroke menu on right, and color palette at horizontal bottom) befuddles me a bit. Probably because I am not a graphic designer and have never used a program like this before. (But yay for me, I did download and install a few fonts from google successfully!) Do I literally need to click the word 'stroke' in the bottom left hand corner? (That feels like a really dumb question to ask but I'm still going to ask anyway.)

Obviously I need to revisit the in-program Inkscape tutorials and manual to see if I can figure things out... but still, any help from anyone would be much appreciated. Thank you.

Okay, so now that I've uplaoded my screen,  I see thin black line around the circle. Yet when I'm in the stroke paint section of the menu on the right, whether I click a color there or from the long color palette on the horizontal bottom, what changes is the fill color, not the stroke or outline of the circle......

Hold Shift-key down to change stroke color from the swatches at the bottom. Check out Status Bar at the bottom of the Inkscape window for any hints/tips+tricks.

Polygon, so just to clarify (because I'm a noob) I'm going to hold the shift-key down while simultaneously clicking once with my mouse on a swatch color from the horizontal swatches on the bottom?

Is that what always needs to be done anytime I want to change the stroke? (The majority of the time I need the fill and stroke color to be the same for shapes or to have just fill and no stroke at all for shapes) but regardless I still need to know how to change the stroke.

In your screenshots (#1 and #3 above), the stroke opacity is zero, the fill opacity is 100 and the shape opacity is 100. You need to change the stroke opacity.

Here's a post where I tried to describe transparency in Inkscape.
https://inkscape.org/forums/tutorials/how-to-select-multiple-objects-having-the-same-colors-at-once-instead-of-selecting-one-by-one-in-inkscape/

I think I have the hang of things now, thank you both to Paddy_CAD and Polygon

Glad to hear you're on track.