Using Fibonacci levels you can determine the probability of a trend reversal for each price level. Fibonacci levels indicate the price level on which a potential change in the trend may occur. The stronger the cluster, the greater the likelihood that the price level is a support or resistance level for the current trend.

If you are into day trading, the Fibonacci levels (or 'fibbos' as they are sometimes called) may be of some use to you. Users of Fibonacci tend to focus on 4 theories - arcs, fans, retracements, and time zones, which are supposed to highlight reversals in trends as price near fibbo lines.

Three most used Fibonacci retracement levels are 0.382 or 38.2%, 0.500 (50%) and 0.618 (61.8%).

Three most used Fibonacci extension levels are 0.618, 1.000 and 1.618. Also 1.382 extension can be applied as well.

Fibonacci levels were not designed to be used alone. They should be used as a confirming indicator or to determine where a change in a trend may potentially happen.
It takes some skill to determine which Fibonacci level is likely to cause the market to turn.
Do not blindly anticipate a market turn at Fibonacci levels.