A chart represents the change in price of a currency-pair over time. The price is the y-axis (shown on the right), and the time is the x-axis (shown on the bottom).
This is a 4 hour chart. Each candle represents the price fluctuation that happened over 240 minutes.
You can see that the price of the USDJPY is going down, it is in a downtrend. This is a great time to be a bear and buy first and sell later.