vent on my macbook

The black strip along the back is the "vent" area.

You should always have your MBP on a hard flat surface to allow air to circulate around the unit.

But also know that the system shuts itself down if it gets too hot to prevent damaging internal components.

Your friend is poorly informed. I'd refrain from taking any tech advice from him.

A MacBook or MacBook Pro does have vents, but they are hidden inside the hinge mechanism. You can see them if you look in there. That reduces the overheating on a surface like carpet, compared to a machine with vents on the bottom... but it's still not a good idea to use a MBP on a soft surface like thick carpet.

As i know from my knowledge about Macs , you don't have to cover vents your laptop . if you want to know where is vent in your laptop , if you have macbook or macbook air , its vent between screen and body of the laptop .

inaddition , you don't have to put your laptop up of cotton or carpet or any thing which has fabrics . Also, keep in your mind that you must care about your processor , don't carry it over it can .

all these what i know , and i wish solve your problem

Yes it can. Never allow the vents to be covered. It needs to be properly ventilated.

Read here > Apple - Support - MacBook Pro - Care and Handling