I cant see any way to reply to the individuals replies I have had above. Thank you everyone for putting things forward. Am totally bewildered at this point, so all ideas are useful. The video is 4 mins long and I spent the whole afternoon going round in circles.
REPLY TO SMADELL
1. It doesn't let me select only mask on the right. It highlights group and mask together. Then they both disappear and I get a list of Pixels.
2. Is it paintbrush I need or paintbrush recolour?
3. I have selected white but nothing happens no matter how long I move the circle round.
4. Thank you for the tip on the crosshairs. I have now got a circle.
REPLY TO KILLZEN
No I am using Mac OS 10.15.4
REPLY TO FIRST DEFENCE
Thank you for this. I don't really understand much of what you wrote to be honest. All I was trying to do was do exactly what it says in the video with the hope that it would gradually all make sense and give me a context for learning something.
I will see if I can work out how to do a video of what my problems are, as you suggested, and try and post that.
The video must be for an older version of the app, is the only explanation I can think of but if they release a new version they should take down old videos that don't work. Then again it could be me. But I have checked that everything on the screen around where the presenter is working looks like his screen. And it does. Until I try to use the paintbrush and then it all goes awry.
Thanks everyone. Hopefully one more day on this will be enough to change eye colour!