The fact that you had to ask this question also tells me you are not prepared to invest - these are extremely basic questions which means you do not have much knowledge as to how the markets work - a sure sign of disaster.
Stocks are not a good investment for someone in your situation.
When you hold quality stocks over a period of time, the prices will go up for a real reason; the companies are earning money every year and becoming more valuable. This is not gambling; you are owner of a money making business.
But it takes time for the business to earn money. Time is not what you have for your money.
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To start trading stocks, you will need to open an account with a brokerage house such as Scottrade or TD Ameritrade. They are required to have you fill out some forms. You must put money into your account before you can begin to order trades.
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Consider how you can invest in yourself, maybe buy tools you could use ins some freelance, handyman wort of work, maybe community college fees, perhaps some how to books or courses on business or a better suit for job interviews.
Just the processing fees for a stock trade takes a while to earn back, assuming the investment does go up.
I can only echo Steve's post. You invest when you have a job for your retirement. Your best "investment" now would be in more education so that you can either get employment or be able to employ yourself.
I am 19, unemployed, but have a couple hundred dollars I've saved up. Should I consider investing in the stock market for a little more cash? Where do I buy stocks or investment bonds?