Although most cameras come with a built in flash, they're not powerful enough for certain shots and you're obviously limited to it's usage. The other problem with the built in flash is that it is fixed facing forward and most of the time especially if shooting Portraits can give the effect of a 'Deer caught in a cars headlights'
However, when using a Speedlight you can rotate the head at certain degrees which is really the best way to use your flash and bounce the light off the wall or ceiling which ultimately gives a softer tone to your images, especially if the wall or ceiling is white. You have to bear in mind when you are using bounce that, if you have a red wall, or blue then some of that colour would be reflected onto the model, a black wall will absorb some of the light. If you are in a building where there are high ceilings or not near a wall then you can improvise with a Reflector or Flash Softbox, there are many alternatives.
A German company called Sunbounce have an excellent product called California Sunbounce - Bounce Wall, which attaches to your camera and enables to bounce the light wherever you are. See website link below.
Photographer using the California Sunbounce - Bounce wall
The Bounce Wall comes with the basic White panel but there are a few others available as well, i.e. silver, gold which all give a nice effect for certain projects. Well worth the buy though.
There are many tutorials out there for posing techniques, flash positioning, light direction etc and a lot of the time it's really all about getting your camera & flash out and practicing with a willing 'model'.