Here you can find few very useful hotkeys which you should familiarize with, if you want to use photoshop efectively
CTRL + N creating new image
CTRL + SHIFT + N creating new layer
CTRL + A select entire layer as selection
CTRL + SHIFT + I Invert selection
CTRL + D deselect current selection
X flips foreground/background color
D default foreground/background color
ALT/CTRL + BACKSPACE fill current selection or entire layer with fg/bg color
CTRL + T turns on Free Transform
CTRL + R shows rulers
CTRL + Z undo