Potting Soil, Dirt, and all the other nouns that can tell us that this is the stuff that we put into the Bonsai Pot to hold the Bonsai in place and to be a holding agent for the necessary water and nutrients so necessary for the health and well being of your Bonsai.
In this arena we have:
Complete Potting Soils which include Akadama, Fujiyama Potting Medium, and Kanuma
Additives or components to make a complete potting medium
And then we have a selection of items that are normally used as a decoration by themselves or sprinkled on top of a Bonsai soil area to cover over whatever you feel that is less pretty called Top Dressings.
Now to make it a little more complicated you can also use some of the above items interchangeably from one category to the next. Like using Akadama as a top dressing over the Fujiyama Potting Medium. It looks great!
Within each category we will explain in detail the reasons you use this or that. As a beginner/novice/just new to the hobby, you should pick a complete potting medium such as Fujiyama Potting Medium. It's like going to the grocery store and buying a store bought cake. It's complete and finished and until you get your hands dirty in making your own recipe of soil components like peat moss, pine bark and calcined clay this is the best first choice.
For those with some experience, try different amounts of each ingredient to formulate your desired potting soil.
It's important to remember, however, that Bonsai potting soil has an entirely different texture than does store bought potting soil.