"this button :def: which is on the right end of the control bar."
That sounds like a tutorial I might have written. It's on the right end of Star, Spiral, and Paint Bucket tool control bars. But as TD says, it appears in many places besides control bars. Also, something might have changed in recent versions of Inkscape, and not many of my tutorials are being updated.
The icon also sometimes looks like a red cross, you need to be flexible in finding things. It is not provided by Inkscape, but by your operating system, and thus may look different for you.
Beginners' Questions How do I get this icon to appear
Inkscape.org
"this button
which is on the right end of the control bar."
you mentioned this in one of your tutorials
It is not on my toolbar
The icon is used in a number of places within Inkscape.
Can you be more specific?
That sounds like a tutorial I might have written. It's on the right end of Star, Spiral, and Paint Bucket tool control bars. But as TD says, it appears in many places besides control bars. Also, something might have changed in recent versions of Inkscape, and not many of my tutorials are being updated.
The icon also sometimes looks like a red cross, you need to be flexible in finding things. It is not provided by Inkscape, but by your operating system, and thus may look different for you.