Marquee Tools (Keyboard Shortcut : M): Useful to select a part of an image in a predefined shape. 4 marquee tools :

• Rectangular Marquee : makes rectangular or square shape selections
• Elliptical Marquee: makes elliptical or circle shape selections
• Single Row Marquee : selects single row of pixels
• Single Column Marquee : select single column of pixels

Selection with Marquee Tools:
Drag diagonally to specify size of selection.
Hold down shift to constrain the shape of selection

Moving selection while selecting:
Hold space to change position of selection while selecting.
If selection was completed, place cursor inside selection and drag

Feather: used to specify the number of pixels at the edges of selection to be blurred. The value of feather should be appropriate to the selection size.

Applying feather:
Enter the value of feather in option bar, if you want to apply it for the next selection
If selection was already completed,
right click on selection–>feather
(or) press ctrl+alt+D

Apply transform: Ctrl+T
Cancel last action: ctrl+Z
Cancel last 20 actions (History): ctrl+alt+Z

Anti-aliased: makes the edges of elliptical or circular shaped selections smooth by minimizing zigzag or staircase effect.

Style of selection:
normal: to select manually
fixed aspect ratio : to select by maintaining specified aspect ratio
fixed size: to select in the specified size.

MOVE TOOL (KBS: V)
Move tool is used to move/copy selected part to another or within image.
Select Inverse: Ctrl+shift+I
Deselect a Selection: Ctrl+D

Creating new image based on selection size:
Make selection
Copy with Ctrl+C then press ctrl+N
Paste with Ctrl+V