Binary Options are traded in assets. These include: commodities, indices, currencies and stocks. Principally you can trade anything which has a variable price over time. This gives you the possibility to trade on something which you know and feel comfortable with before moving on to other areas which might be of interest for you.
Examples of Binary Options include:
You can also add stock pairs to the list above. Where you bet on the price difference between the prices of two firms stock prices over time. Each broker will have a different number of assets which are available to apply your Binary Options skills on. Some have only a handful while others are having over 150 to choose from.