The smart brush tool is similar in use to the Pull tool, but is better at fine detail work. In simple usage, you pull from an existing selection to extend it, just like the Pull tool. You can lock selections in exactly the same way as you would with the Pull tool.
There are 3 different modes for the smart brush, that can be switched between using the drop down next to “Find”. The brushes can be switched between using a keyboard shortcut as indicated by an underline in the dropdown.
Solid, Opaque Areas will look for larger, hard edged areas, like branches or girders.
Feathered, Translucent Areas will look for edges that are not well defined, or objects that are either partially or wholly translucent. For instance, use on grass, and finer edges to trees or plants in the distance.
Everything inside brush stops the brush being ‘smart’ and looking for edges, like a normal solid brush.