What it measures
The Relative Strength Index compares the size of recent gains with recent losses over a number of periods — 14 is the usual setting, and the one SignalVexa shows. It produces a value between 0 and 100.
Readings above 70 are often described as overbought and below 30 as oversold. Those are labels for strong recent momentum, not predictions.
Limits
In a strong trend RSI can stay above 70 or below 30 for a long time. Many traders read it alongside price structure and other indicators rather than on its own.