http://stevecampbellhillwood.blogspot.com/2015/12/photoshop-tools-explained.html
Be sure the Mode is Brush and the Hardness is zero % (0)
See graphic below
Pick a brush size that works best with the area you want to erase.
See graphic below
Follow the information in the graphic below:
The best way to Zoom In and Out is to use the Navigator Tool. Go to Window>Navigator.
