One learns the basics of bonsai best by creating them, even your first one. Without these basics, it is unreasonable to expect that someone could keep one alive, let alone maintaining it as art. There is also the cost factor. Any 'real' bonsai will take at least five years of development to be convincing.
To buy such a bonsai would cost several hundred dollars. Of course you can find 'mall bonsai' everywhere, even grocery stores. These are junk, they are not bonsai. A two year old juniper cutting plunked unceremoniously into a bonsai pot is not bonsai. It is the care and training that makes bonsai; these plants have none.
If this seems daunting, well, it is. It takes years to learn most bonsai skills, well, two years to learn the basics anyway. Styling skills are learned over a lifetime. Well then, how do you start? First and foremost read as much as you can find about bonsai. My website is a good start, there are many others. Join the Internet Bonsai Club. The instructions are at Links. Next look at as many bonsai as you can, even if only pictures.
Many images are available on the web, analyze them critically. Try to determine just what it is that you like about them. Until you can visualize bonsai, you won't be able to create one. But you can begin by copying and following the Rules. Get a book or two, first a simple book, like Sunset's "Bonsai", then a good book like John Naka's "Bonsai Techniques I".
Begin right away. Buy one gallon nursery plants that look interesting and start training them. Don't even repot them. This is important. Virtually all beginners are impatient to get them in bonsai pots. Good bonsai don't go into bonsai pots until they are basically finished. Finished is a relative term in bonsai because they are never really "finished". Don't pot it until the trunk has reached the size and shape that you desire. This is after at least a few years of training; the best and largest don't go into pots until after twenty years or more. If you work on the roots right away, you will kill it outright. But by working on the top you will learn some of the pruning, wiring, and styling techniques, and will actually prepare it for its first root pruning. It may die anyway, so be prepared for that.
It is a necessary part of learning. After a year or two you will have some inclination about how to deal with the roots, so don't worry about that now.
Take this nursery plant and style the upper portion of the plant by pruning. What you do and how much you remove will depend upon the time of the year, but if you go slowly and don't remove more than about a third of the foliage in any one session (with a few months recovery in between), you will be pretty safe.
Your plant should thrive and become compact. Slowly it will begin to look more like bonsai and less like a bush. There are many, many, tricks and techniques to pruning and styling. You can learn these by reading about bonsai, but mostly by looking at them and visually analyzing them.
One of the first things you will notice is that all of them have a definite trunk line. It usually will be a single trunk, but sometimes there will be a dominant trunk and a secondary trunk. Rarely will there be more than two trunks except for group or forest styles. Your nursery plant will have many trunks and branches if it is a shrub, but a single trunk if it is a young tree.
I recommend that you get a shrubby plant first; it will give you more to do from the very beginning. One of your first tasks will be to find a trunk line. You will have to visually eliminate all the unnecessary trunks and branches to see the trunk line. In fact this should be the basis for the selection of the plant in the nursery. In a shrubby plant there is rarely only one 'bonsai' in a plant. Your job is to find the most pleasing trunk line. It most likely will not be straight but rather curved with flowing movement.
After you take your plant home you can begin the job of revealing the trunk line by removing competing trunks and branches, but before you do, give some thought as to which branches you will want to keep. There are conventions for this too, but the easiest to remember is that the branches go on the outside of the curves. If you only do this, you will have a plant that will resemble bonsai and already be miles ahead of the typical $29.95 mall bonsai.
Continue to refine your plant by pinching back the new foliage to force more growth closer to the trunk and to make it denser and more compact. One of the things that you will quickly discover about bonsai by looking at them is that the foliage is nearly always carried by branches to form distinct foliage pads separated from each other. This is quite intentional. You should pinch and prune to form pads.
Remove anything growing up out of the pad and remove anything growing below the structure of the branch and its secondary branches (which are usually in a flat plane). Lastly, prune your bonsai so that it forms a scalene triangle of foliage. That is a triangle with unequal sides, angles, and make the three corners of the triangle occur at different levels.
If you can do all this and keep you plant alive in its nursery container for a year, then you will probably be ready for the second phase of learning root work. You will have a healthy compact plant with excess root capacity ready for a soil change and root reduction. But in the meantime read all you can to prepare. Try to find a club in your area; it will help immensely. In a club you can repot with expert guidance or simply watch it done a few times before you attempt it.
Of course everyone wants bonsai inside, preferably on their coffee table, but bonsai is basically an outdoor activity. Even in the northern reaches of Canada, there are folks who grow outdoor bonsai. They must be protected in winter, but even after learning how to protect them, it is easier to grow outdoor bonsai outdoors rather than indoors. Indoor bonsai is quite difficult and is limited to tropical species. If this is your only option, or inclination, stick with Ficus species, they are cheap, easy to find, and can withstand a lot of abuse. You can also find some that already have decent size trunks that are reasonably priced.
Hopefully you have discovered that you can click on the highlighted links to find out more about those topics. Let's review up to this point:
Don't buy your first bonsai.
Select a one gallon nursery plant for your first victim.
Prune and style the top of the plant into a shape that pleases you.
Do not repot or prune the roots.
Keep your plant outside, even in winter (with protection) unless it is a tropical.
Still don't know what to do? Go back and read this article again, INCLUDING the topics that are highlighted. There is an enormous amount of material to be digested here. I have made it as simple as I possibly can, but the rest is up to you. Believe me, EVERYTHING you need to know to start bonsai is right here in front of you. Nobody said it was going to be fast or easy, but it is fascinating and addictive. If you have the dedication, it can be done.