Trend lines are drawn on charts to help predict the general direction of price.It also help to determine good entry and exit point.they also help to see the reversals.
A trend line is a line by which a trend goes on respecting. Whenever the market touches the line it goes again to the trend and continue to trend. This is a way a trend line works. So this is what a trend line is and it is very powerful tool you can use if you want to make money in the forex market and you must draw it properly.