selecting wispy hair questibn

Was watching a tutorial on selections, and the presenter was asked  a question about wispy hair. The presenter quickly answered the question by stating  basically --to use  channels to make an initial selecin ( Iunderstand that)---then paint on the mask in overlay mode .    Can anyone elaborate on"painting on the mask in overalay  mode"y to complete the selection--a link to a tutorial maybe...

I am quite familiar with making  difficult selections- but not totally familiar with this particular technique.

Thanks

Buzz