Lucy,
the easiest way to learn how to use the flash outdoors is to use the flash outdoors. Today's camera/flash combos have so much computer power behind them it's almost impossible to make a mistake. Once you're comfortable shooting with everything on automatic, then start experimenting with manual exposures of the camera and, eventually, couple that with manual exposure of the flash unit varying the power so you can open up your lenses for shallower depth of field.

The great thing about digital is that when you experiment, you aren't burning up rolls of film which you then need to send out to be processed, wait and then review the prints/slides. With digital, you're only wasting your own time and talent in an effort to get better. Besides, experimentation is fun.

So, try some stuff and see what you get. If you like it, you're doing fine. If you don't, figure out what you don't like and make some adjustments. Or share it with the troops here and we'll tell you what we think the problem is.

But most of all, have fun. After all the business of being a photographer, if you aren't having fun when you shoot then you need a new hobby.

Jim