Black pixelation on my images?

I take a picture of a windows in my house, when I review the image of the LCD screen, the space between the blinds show black pixelation that flickers. What I'm doing wrong? Is it the camera settings or the camera itself. It's pretty consistent with the windows.
Camera is a DSLR Nikon 5100

Added (1). Sorry for typos

What you are seeing is the "Highlight Blow-out" warning. This will flash black and white in areas of the photo that are blown out to pure white (255 on Adobe colors).

You are doing nothing wrong if you want to have that area pure white. But if you are wanting to go back in post processing and recover some of the blown-out, you will not be able to. You can turn "highlight warning" off if you want.

The camera is metering for the indoor area. There's a vast, huge, tremendous exposure difference between the indoor light and the bright outdoor light through the window. The camera, NO camera, can expose for that much tonal range in one photo. So the monitor is telling you that the outdoor area is going to be completely overexposed, thus the highlight warning flashing.

You either have to expose for the outdoors, in which case the indoor area will be too dark, or expose for the outdoors and use flash indoors to try to compensate for the exposure difference, or use HDR technique in which the camera is mounted on a tripod and several photos are taken with various exposures so both the indoors and outdoors is properly exposed. These photos are then merged into one overall correctly exposed photo in software.

Has it occurred to you to read your manual? You would have known about this feature already, plus you would have a learned a whole bunch of other useful stuff, too.

Experience taught me that you'll now say: "I lost my book, that's why".
Well, you managed to use the internet to ask this question, so now use it to go the manufacturer's website and download an electronic version of the manual.

READ THE MANUAL, there's a reason for its existence!