Transform means changing the form. With transform we can resize, rotate, skew, distort, perspective and flip the selected or selection.

Apply Transform:
Edit menu–>Free Transform (Ctrl+T)

In transform mode we can see:

• bounding box
• resize handles
• proxy/base/reference point
• upon the selected image.

Options in the options bar while transforming:

• proxy points
• screen coordinates of selected proxy point
• dimensions of the selected image
• Rotate
• Horizontal skew
• Vertical skew
• Apply and Cancel buttons

With transforming we can:

• move
• resize
• rotate
• skew
• distort
• perspective
• Flip

To come out from transform with saving:
press commit button on option bar
(or ) press ctrl+Enter (alphanumeric keypad)
(or) press Enter (numeric keypad)

To come out from transform without saving:
press cancel button on option bar
(or) press Esc key

To apply transformation to selection:
Click on Select menu–>Transform selection
(or) alt+s+t