What are some good features of camera for portraits?

I'm a newbie and my budget is $500
is it mean that its good when its got a lot of megapixel?
what do you think of Nikon D3100?

I'm a Canon guy so that's all I recommend.

Portraits? There are no specific "good features" for a camera to take portraits… At least not among
the current run of dslr cameras anyway.

A good lens is most important. I use a 50mm f/1.8 for portraits. I'm shooting in available in home window light and this lens does a very good job at it.

Out doors, your 18-55 that comes with the camera will work just fine.

The D3100 comes with a 18-55mm lens & is a very good camera / lens setup to start with.
You can get the D3100 for around $450. Add another $20 for a class 10 8GB memory card and you're ready to go.

If you are cheap or can't afford a "stable" of lenses then look at a quality "bridge" camera such as the Pentax X-5. This is a bridge camera with a permanently attached zoom lens capable of everything from macro, to wide angle, to portraits, to long distance scenes. It sells for about $200.00 and that's it. With a DSLR you will need a Portrait lens $215.00-to-$400.00.in addition to the lens (usually 28-55mm) that comes with the camera. So you are looking at $700.00 to $900.00 for a DSLR and a decent portrait lens. If you want to econmize even more, get the camera with a 28-555mm zoom lens and add a Tiffen Warm Soft FX3 filter @ $48.00.

Any camera will do. The camera is only a tool. What's important is you know what you're doing.

The D3100 is a dSLR. DSLR's are very good tools for taking pictures. It doesn't make the user take great quality pictures automatically though. You still have to know exactly what you are doing.

Megapixels only tell picture size. 6MP is enough for most everybody. Megapixels have nothing to do with picture quality. You have to know exactly what you are doing.