At its simplest you buy a pack from the supermarket, put it into the breadmaker with the correct amount of lukewarm water and switch on. A 2lb loaf will take about an hour to bake.
At the other end of the scale you can start from strong (i.e. gluten-containing) flour add water, salt, yeast and maybe a few extras - some oil or butter may be called for, milk powder can also be used, wheatgerm, cornmeal etc - it all depends on the recipe. There are some very good breadmaking books available with recipes from all over the world.
You can use the breadmaker to mix and bake many of the recipes. Others may just use the machine to produce a dough and you can carry on and do the baking in a conventional oven; plaited and flatbreads for example. It also takes a lot of the effort out of mixing up pizza dough!
In terms of flour treatment agents they may be used, particularly in the pre-packed breadmix varieties, but they're certainly not necessary in every case.
The one disadvantage I personally find with a breadmaker is that there is always a little paddle in the bottom of the pan which does the mixing/ kneading. When the loaf is baked in the pan the paddle is baked into the loaf and it leaves a hole in the bottom - most annoying when I toast the centre slices - the honey falls through!