Student credit cards are typically meant for students over 18 years of age. However, until you turn 21, getting one comes with additional requirements (you need to show that you earn adequate independent income or have a co-signer). You might consider getting a student credit card if you want to start building your credit history, if you need short-term financial assistance or if you want to safeguard your spending when overseas.
You can use a student credit card to make all types of legitimate purchases. However, you should pay them off as quickly as possible to keep your interest charges minimal. Compared to regular credit cards, alternatives for students tend to have more relaxed creditworthiness requirements.