Servo motors can move like robot arms.
it's used to move things to specific positions. Imagine you have a toy car and you want to turn its wheels. You can use a servo motor to do that.

Ultrasonic sensors measure distance like magic rulers.
Imagine having a tiny bat that helps your Arduino "see" objects around it without using eyes. That's what an ultrasonic sensor does!

Potentiometers adjust things with a twist.
Imagine having a volume knob on a radio that you can turn to make the sound louder or softer. A potentiometer, or "pot" for short, is like a knob you can turn to control things in your Arduino projects.