Line chart

By plotting the price of a currency pair over time on a graph and drawing a line through the points you get a simple line chart.  The data from a chart like this is limited by the timescales set.  So the points could be the closing price once a day if you are looking over the course of months or years or the price every minute, to every single price movement in fractions of seconds.

Bar chart

A bar chart allows you to plot more data on the same area than a simple line chart.  Rather than just have the closing price for a particular day, a bar chart shows the opening price, the highest price and lowest price for that day and the closing price.  Once again the timescales can be set arbitrarily so a single bar can represent a day, a week or whatever other unit of time is required

Candlesticks

Candlestick charts are another popular chart format.  They provide the same data as a bar chart but in a format that is visually more appealing.  They are easier to read and generally more favoured than bar charts as it is easier to spot patterns

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