Yes, the camera comes with a small flash that you attach to the socket on the top of the camera. You flip it up to turn it on. It works well with the standard lens, but it's too small for the larger telephoto lenses. It's great for indoors and for some fill flash, but the HVL-F20S is a *much* better, more powerful flash that works with wide angle or telephoto lenses.
I have the NEX-5N which came with the Sony HVL-F7S Flash unit and allows you to select:
Auto Flash (which automatically fires the flash if your subject is dark or backlit);
Fill-Flash (which always fires the flash);
Slow-Sync (which slows the shutter speed and fires the flash for clear images of both the subject and background);
Rear Sync (which fires the flash before the exposure is completed, creating a path of light behind a moving subject);
And Flash Off (which prevents the flash from firing at all).
As an accessory item, there is also the Sony HVL-F20S External Flash. Sony says that this flash "extends the range of your NEX camera's included flash and offers bounce flash for shadow-less indirect lighting. You can find more information on the HVL-F20S at their website: http://store.sony.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10551&storeId=10151&langId=-1&productId=8198552921666347923
Absolutely but I prefer not using it unless pitch dark. I prefer the more natural lighting without even if it means more noise in very low-light situations...But it attaches to the strap in a small case so you'll have it with you at all times...