Mode S (Shutter-Priority Auto) - Nikon D3400 Reference Manual

Mode S (Shutter-Priority Auto)

This mode lets you control shutter speed: choose fast shutter
speeds to "freeze" motion, slow shutter speeds to suggest
motion by blurring moving objects. The camera automatically
adjusts aperture for optimal exposure.
1 /
Fast shutter speeds (e.g., s) Slow shutter speeds (e.g., 1 s) blur
1600
freeze motion. motion.
To choose a shutter speed:
1
Rotate the mode dial to S.
Mode dial
101
P, S, A, and M Modes