Canon EOS REBEL T3 Basic Instruction Manual page 157

Shooting Tips
Change the ISO speed or use the built-in flash.
To match the subject and ambient lighting level, you can change the
ISO speed (p.77) or use the built-in flash (p.88). In the <d> mode,
the built-in flash will not fire automatically. So under low light, press
the <I> (Flash) button to pop up the built-in flash. (You can also pop
up the built-in flash by selecting the <s> icon on the Quick Control
screen.)
The program can be shifted. (Program shift)
After pressing the shutter button halfway, turn the <6> dial to
change the shutter speed and aperture setting combination
(program). Program shift is canceled automatically after the picture
is taken. Program shift is not possible with flash.
Differences Between <d> and <1> (Full Auto)
With <1>, many functions such the AF mode, drive mode, and built-in
flash are set automatically to prevent spoiled shots. The functions you can
set are limited. With <d>, only the shutter speed and aperture are set
automatically. You can freely set he AF mode, drive mode, built-in flash,
and other functions (p.232).
If he "30"" shutter speed and the maximum aperture
blink, it indicates underexposure. Increase the ISO
speed or use flash.
If he "4000" shutter speed and the minimum aperture
blink, it indicates overexposure. Decrease the ISO
speed.
d: Program AE
73