I pressed something by mistake and this symbol appeared with a number 1 next to it. I don't know what it is abd I want to get rid of it but I can't select it or right-click it - does anyone know how I can get rid of it? Thanks!
That is a fixed measurement with the eyedropper tool. You can add them by using Option / Alt and clicking the area you want to measure. (Handy if you are making precise adjustments to color in a file). To remove them simply use the same command combination and hover over each sample until you get the scissors, then just click to remove.
Sorry, if I press Alt and right click the symbol temporarily turns to a red dot but I can get a scissors symbol to appear and none of the righ-click menus seem to allow me to get rid of the symbol, could you explain again, please?
I think that is "left click" not "right click", but another way is to go to the Option bar at the top and click the "Clear All" button.
Then press and hold on the Color Sampler tool in the Toolbar, and other eyedropper tools will fly out. Select the one you normally use. Another way is to press "Shift i" to cycle through the eyedropper tools. I think that was the combination you accidentally hit.
Shift and any one-letter tool shortcut will switch tools in that group.