Candlestick
A Japanese candlestick shows price action over a period using four values: open, high, low and close.
Each candle has a body and wicks. The body connects the open to the close: it is usually green or white if the close is above the open, and red or black otherwise. The wicks show the extremes reached during the period.
A candle can cover one minute, one hour, one day or one week, depending on the timeframe you choose. A daily EUR/USD candle sums up the whole session.
Reading candles means reading the battle between buyers and sellers: a large body shows clear control, a long wick a rejection, a small body indecision. Their meaning always depends on where they appear.