It is pretty easy. Best thing to do is to practice on a extra piece of sheetrock/wallboard first.
Buy a large Natual Sponge, not a store/kitchen sponge. But different sponges will give you a different look.
Wet the sponge and wring it out before starting. After you touch it in the paint and before you touch the wall blot the sponge off on newspaper. After a few practice blots/touches you will get the technique. Use a light touch and random movements or it will be strip-y.
Dark wall with lighter color over it is a softer look.
Light wall with darker color over it is a brighter louder look.
If you go back over a bright look with the base color you can soften the bold look, if it is too bright.
Our local Fleet Farm carries sample packets of paint, like 3 oz, look for some of those for experimenting. I think the little bottles of stencil/ceramic paints would work too. At least to experiment with colors and techniques.
Go For It!