From your post I see that you don't have any experience in starting a business. There is no "easy" way to this. We dont' know your financial situation, how you're established, what resources you have, what type of computer business this is. It's like saying "i want to be rich, what do i do?" A VERY ROUGH sketch of what you should look into should be as follows:
You can't just "start" a business. You need a business plan (which is a detailed account of every aspect of your business, from its goal to expected profits, losses, job descriptions). You can find samples of those online. Assuming it's good, you can get financing from a bank. Unless of course you can find other sources that will invest in your business...parents, friends? You'll need a business plan either way. The business plan outlines every aspect of your business, you'll need it more than anyone. If you dont' know what's going on, then you're screwed. I'm not even going to go into it, but a good portion of the costs would be on advertisements alone. If no one knows you exist or that you're reputable, your business will be out of business. I also suggest you get some legal advice, especially if your business is actually going to be on paper and not something along the lines of fixing computers for friends and charging them. Liability is your main concern since I assume you're going to be selling either a product or a service, you'll be responsible for what you develop. If your business starts to make a profit you should incorporate (no liability on your part), again, you'll need to get legal advice. But as I said earlier, there is no "easy" way to go about it especially if it's a "side job". Since it's your own business you'll have to devote a major part of your time in any given day. As an example established computer companies like Gateway have gone out of business near where I live.