Why does Nikon D3200 have got 24.2 MP but sold for only $500?

I'm looking to buy a camera and interested in this one.
i'm a beginner, looking for the one that's good for portraits.
is Nikon a good brand?
please advise me.

Nikon and Canon are the top brands and are the ones the pros use.

Why?

Because they have the most lenses and accessories available and are the only ones that make high end cameras robust enough to stand day in and day out shooting

You really need to visit the Nikon and Canon websites, read the professional reviews of the entry level cameras like the D3200 and T5i/700D on the DP Review webstite

Finally you are going to have to visit a proper camera shop and hold your choices in your hands

Megapixels only tell picture size, not picture quality, not camera quality. Nikon is a good brand for dSLR's and lenses. Why is the D3200 cheap? It's a bottom of the barrel model.

Megapixels are not and have never been a measure of image quality.

Camera companies, or I should say their marketing departments have done a great job of making people think more is better.

The D3200 is an OK dSLR, but nothing more. It's unremarkable. The extra pixels means more noise in low light. Look at a Pentax K 30, K 50 or Sony Alpha A57 or A58.

Nikon fanboys are going to tell you that Nikon rules and that this camera is amazing. Both are not true. Canon and Nikon are the Honda and Toyota of the camera world, they sell cameras mostly on the name brand, they stopped tying to innovate years ago.