Use of Monitor Output Socket

Question

I would like to use my Sony Vaio laptop for a powerpoint presentation on my college course.
I have tried to plug in the overhead projector cable to the monitor socket to the rear of my laptop, but do not know how to enable this output. For information a friend's Dell Laptop will drive the same projector by him typing the Fn and F8 keys.
Please can you advise if there is a similarly simple procedure for this Sony Vaio laptop?
Many thanks
Frank Bailey