How can you start your own online business? Any good suggestion?

Find an need in the world and fulfill that need (make sure it's something people are willing to pay for and will do repeat business). If you have a small or no budget, providing a service is the best type of business so you don't have to have inventory. If you've never run a business volunteer at a small establishment to understand the day to day responsibilities sells, marketing, book keeping, advertising, customer service. Or start out as an independent sales person for an established brand like (Mary Kay, Avon, Tupperware) do that so you can earn/save money to finance your business) & find out what makes a good business work (then branch out on your own).

No, that is your major job. Find something you can offer that is better, faster, bigger, cheaper than others offer. If you try to sell the same thing others have, not much potential there. It should be something you have a strong interest in.

What business do you want to involve? sell product that are in demand on ebay. do some niche market research.