This is an image from the Gary Fong product (I'm not advocating the product, just the technique) :
left : direct, pop-up flash
middle : hot-shoe mounted flash (speedlight), tilted to bounce light off the ceiling
right : hot-shot mounted flash with their diffuser
Note the "raccoon eyes" of the middle photo. This is typical of the ceiling bounce if the photographer is not careful to avoid it.
With just a hot-shoe mounted speedlight, the lighting choices become (almost) endless. You can bounce the flash off walls, ceilings, behind you, etc. Each of these helps to make the source of light much larger than the "point" source of the camera pop-up flash, which softens the shadows.
This can be a pretty in-depth subject, but the more you read the more you'll learn. The links above are good sources of info.
I also want to recommend this book :
Amazon.com: Light: Science and Magic: An Introduction to Photographic Lighting (9780240808192): Fil Hunter, Steven…