There are a few things you need. The first two requirements is that you are over 18 years old and have an income or a co-signer on the account with a monthly income. Credit card companies don't want to lend you money unless you have a monthly income to support it. The other things you need is a social security number, which allows the credit card company to identify you, and also a credit history. A credit history is the history of your previous loans. The better your credit history, the better credit limits and interest rates you can get on the credit cards. It shows that you are more responsible over time with your money and intend to pay it back to the company.
Credit cards are safe, but you should make sure you don't share your credit card number with anyone. They can easily steal your identity and illegally charge things to it without your permission, which can cause financial disaster if you don't have the money to pay for it!
Money Smart Kid