Once a selection has been created, you can refine its edges to ensure your selection is as accurate as needed.
For very fine selection, e.g. of hair against a coloured background, use an adjustment brush as part of the refinement to 'brush-in' fine detail.
The following settings can be adjusted from the dialog:
Selection and Mask are ideal when applying adjustments and filters after refining the selection area. New layer and New layer with mask are suited to cutting out and compositing; colour 'decontamination' is also used for achieving high-quality cut-out results.
Brush size can be adjusted mid-stroke with the [ and ] keys.