Dodging
This technique allows you to lighten a portion of your image by not exposing it as long as the rest of the picture.
Expose your print for a few seconds less than you would normally do. Then
hold an opaque object (like your hand) over the selected spot and turn on
the light for the remaining time. Quickly move the object back and forth to
prevent an edge from forming. Make test strips of both the main image and
the selected portion to determine the lengths of exposure.
Dodging process
Normal Photo.
Notice how dark the trees are.
Trees have been dodged.