Trying to make money here from other members isn't very wise unless you have a large following of fans already. Even then most have to work their asses off to do a lot of commissions, because most members are just teenagers with very little money, and many expecting to only pay with Points that were donated to them by their friends/watchers.
The best thing is to work up a good portfolio of various work that shows you have the ability to work in different styles and/or mediums. Then scour the Job Offers forum for any jobs you think you can do, give those clients a link to your portfolio (an offsite, professional looking portfolio would be best) and keep applying until someone hires you. You should also do some good research on how to conduct business, such as fair contract agreements to protect yourself and not doing work without being paid first. Many kids get taken advantage of by being asked to draw or design something for free with some excuse about why and then a promise to pay you if they like your work. Never fall for that. The whole point of making a portfolio is to show clients what you can do. If they can't decide if you're a right fit based on that, then they're probably a client you won't want to work for.
As for getting stuff in your portfolio, there's plenty of free resources and stock images for you to work with here on dA. You don't have to buy stock. If you do art at school, you can use that too. It would also help to learn how to take your own photos or work on your drawing/painting skills. And don't just stick with dA as the place you look for jobs. Put yourself out there for anyone anywhere. The best thing you can do is start by getting work from friends, family, and acquaintances that will refer you to other people. Otherwise try to get a regular job with a company.
thank you for your kind reply. I do need to make better portfolio, but most of my friends acquaintances don't buy art. I discovered that I liked doing photomanip, few years ago, but again it was late for me to start studying it properly. Right now, I am practicing as much as I can in order to grow.