How to take a screenshot on an Nikon D90?

I used the camera to take a video of my family vacation and there's a certain point in the video where i really want to take a screenshot of it BUT i don't how://

Is there even a screenshot button on the camera?

Added (1). I need to know how to take a screenshot on the ACTUAL camera

You take the screen shot while playing the video in the computer, not in the camera.

Yes, you can take a pic of the screen while playing the video. For a better job, use the software that is playing the video to take a screenshot.

If you have the idea of watching the movie on the camera and grabbing a frame at the appropriate point, then that is not possible on any normal camera. The manufacturers build to a specification, and put in enough circuitry to produce correctly focussed and exposed shots which are then safely stored. You are hoping for computing power that the manufacturers do not need to build in.

Most decent video players are able to take frame grabs. Look in to VLC or Media Player Classic as decent video players. MPC is a bit easier to do frame grabs than VLC.

Play it and take a screenshot.

Not sure but download it your computer, play it and take a screenshot.