Technical analysis uses charts to visualize trends in security prices over time. There are three main types of charts - line charts show closing prices connected with straight lines, bar charts show the high, low, and closing price for each period through bars, and Japanese candlestick charts also show open, high, low, and closing prices. Closing prices are the most important for analysis as they represent the end of day price and are used in most techniques. Charts help analysts identify patterns and trends to inform trading decisions.