Click on the color you want and adjust the size, click on the 'erase all' button to erase the entire canvas and 'eraser' button to erase only some parts of your drawing (can adjust the size of the eraser too). Check out my other project - (Draw Anything) - https://scratch.mit.edu/projects/920510829/ - Revealing 2 of my drawings - https://scratch.mit.edu/projects/935265349/ -Decorate a Christmas tree - https://scratch.mit.edu/projects/935270317/
If any problem like if the pink button is clicked and another color comes do inform me.....