The spot removal tool looks like a big O with an arrow pointing to the right. It can be found in the Develop panel, in between the crop tool and the red eye tool. When clicked, you will see an option to Clone or Heal the spot. You can also adjust the size of the area and the opacity you want to use for the removal. Typically I use "Heal" and adjust the other sliders to match the spot. The really nice part of this tool is that Lightroom will try to fix the spot on its own by finding a matching area! However, if the fix is bad you can just drag and drop the matching area to find one that works. Simple, right? It really is!