To
draw a straight-edged selection border when no other pixels are
selected, press Alt (Windows) or Option (Mac OS), and click
where segments should begin and end. You can switch between drawing
freehand and straight-edged segments.
To erase recently drawn segments, hold
down the Delete key until you’ve erased the fastening points for
the desired segment.
To
close the selection border, release the mouse without holding down
Alt (Windows) or Option (Mac OS).
(Optional) Click Refine Edge to further adjust the selection
boundary or view the selection against different backgrounds or
as a mask. See Refine selection edges.