Selection Tools are:

Before selecting:

• Shift+Drag: To change the marquee to a square or circle.

• Alt+Drag (Option for Mac): To drag marquee from it's center.

• Alt+Shift+Drag(Option for Mac): To drag selection from it's center and change it to a square.

• Holding downSpacebar:  to change selection position.

After Selecting :

• Shift+Drag: to add more area to selection.
• Alt+Drag (Option for Mac): to subtract from selection.
• Alt+Shift+Drag(Option for Mac): to have intersected area only selected.

selection in rectangles

selection in ellipses

selection in 1-pixel rows

selection in 1-pixel column

Tools Options

• Shift: Holding shift while dragging to produce a  45° Movement.
• Alt+Ctrl (Option+Command): It copies and moves the new copied shape at the same time
• Alt+Ctrl+Shift (Option+Command+shift): To copy shape and move it in a 45° Movement.
  
  

to drag selections, layers and move them to a new place on the image you're working with. Can also be used to align shapes and layers together.

• Shift:  to add more area to selection..
• Alt: to subtract from selection.
• Alt+Shift:to have intersected area only selected.

Magnetic Lasso: Selection snaps to the edges of  the image that you want to select.

Polygonal: Selection is drawn in straight lines

  Lasso: Selection is drawn in a freehand-like method.

Used to help in painting, while selecting an area the round brush tip expands and find the edges of the image.

• Shift:  to add more area to selection..
• Alt: to subtract from selection.
• Alt+Shift:to have intersected area only selected.

Selection based on color difference in an area. Can be adjusted by it's tolerance.