Help?! Infrared sensor as input motor as output

I'm trying to use an arduino in part of my installation work at university.
My intention is to use an infrared sensor as an input, when Motion is detected to activate a motor that will move 90degrees counterclockwise and delay for approximately 4 seconds before returning to its original position and looping that sequence when motion is again detected.
I have a very basic understanding of coding and have done some playing around with blinks digital and analogue inputs and was hoping for some basic guidance on where to start. Any help would be greatly appreciated...

was hoping for some basic guidance on where to start.

Start by learning how to read from the infrared sensor.

Follow that up by learning to move a servo or motor.

Follow that up by learning to use millis() to record when things happen. Follow that up by learning to use millis() to see how long it has been since you did something.