What makes Elliott Wave theory a powerful prediction tool is (1) repeating and recognizable patterns and (2) repeating ratios between different waves. First you recognize a trending ( so called impulsive ) or corrective pattern and then you simply have to count five waves in any trending move and counter check your count with very specific rules applying to any five wave fractal. 

The theory has a set of very strict and clear rules about allowed depth of pullbacks in a trending moves. That provides you with opportunity to find high probability reversal zones and set precise stop orders to protect your capital in case your count is wrong.

Because waves in the Five Wave fractal follow a number of specific ratios a trader can make confident predictions about areas where waves may get terminated.

To make those predictions you measure waves on the charts and project the distance multiplied by a number of repeating ratios. It only takes you a moment to do that. You just click the lowest and highest points of preceding completed waves. Fibonacci projection and retracement drawing tools are standard instruments available in any charting platform including Tradingview which is probably the best free charting on-line platform.