Fibonacci retracement is usually used to measure a correction of a prevailing trend. Using these ratios, we can often have an expectation of where a correction will likely complete.
Practical Exercise
1) Pick a currency pair, it can be any currency pair, any timeframe.
2) Based on the most recent development in price, apply the fibonacci retracement tool.
3) Post your exercise on the comment section in this thread.
4) Repeat this practice to gather a total of 10 examples.