Technical analysis is the study of price action, meaning you work exclusively with charts. Technical analysts believe that if you study the past moves of prices, it will help you successfully forecast where prices wil be in 5 minutes, tomorrow, the day after tomorrow or even next year. Sometimes they get it right, sometimes they don't. Sitting glued to your computer and studying the charts, you could "discover" patterns and trends that could help you find good setups for successful trades.
The most important thing in technical analysis is the trend! The trend is your friend, as they say. Why is it so important? Because that's where the big money is. If you can "catch" the direction of the trend on time, you could make loads of pips. (This strategy even has a name; it's called "trend following".) Technical analysis can help you determine the trend in its infancy and provide many profitable trading setups.