How to use laptop as an external monitor?

I have a Macbook pro and a Nikon D3300 and I want to use my laptop as an external monitor how do I do that?

You could try connecting the HDMI ports via HDMI cable between the devices if they support it. You could try connecting both through bluetooth and try to use the other device's monitor for the other. You could try connecting them with a USB cable though i don't know if that would work.

Well unless your laptop has a " video in " port and I doubt you do… Most laptops only have a video out port…
Now as for the camera… Does it have software and in that software allow you to do that? So you can connect the camera to the computer ( probably thru USB ) and view what is on the camera screen…

When in doubt, READ THE MANUAL. Here is the online version of the manual that came with your camera--> http://download.nikonimglib.com/archive2/E7vrv00ZwHJt02sHgtZ15XIHOb30/D3300RM_(En)03.pdf

Start reading at page 201.
Stop reading at page 206.

Even thpough the camera came with Nikon software, you can also use Apple software, such as QuickTime Player X, to view movies and iMovie to edit them.

Most pc's do not have HDMI IN so connecting via HDMI is not possible. They also don't have Video in so connecting via video is also not possible so you are left with whatever features the USB port allows. This article seems to cover it http://www.diyphotography.net/introduction-tethered-shooting/