Choosing an Online Trading Broker
You will need to set up an account with an online trading broker such as TD Ameritrade, Interactive Brokers, or a number of other trading brokers.
Here is a very useful article that can guide you through the process of selecting a good broker: Choosing an Online Trading Broker.
Introduction to Risk and Risk Management
Risk is the amount of money you are willing to, and could possibly, lose if your trade or investment is not successful.
Read the complete article on risk and risk management: Introduction to Risk and Risk Management