HC-SR04 not work

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I made a robot otto ninja APP code on esp 2866 LOLIN board (Wemos) D1 mini clone.
What is the actual function of the HC-SR04 sensor? .
I have it connected to D1-Trig and D2 Echo and power supply +5V and GND. I do not see any reaction to the obstacle during the robot's movement. It also does not respond to hand gestures.

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My second question. How do I programmatically adjust a 360-degree servo to stand in the "0" position when the robot is not moving? In my case, LF is rotating and RF is stationary, position "0". I'm talking about the case when the robot is standing still.