This depends on the market you're trading.
To work this out, tap on a market you're interested in and tap the "i" in the top right hand corner.
In the market information look for the "Underlying unit risk", this will tell you which part of the price you are trading e.g.
EUR/USD states 0.0001
This means, the 4th decimal effects your profit or loss. So, whenever the market moves from 0.0001 to 0.0002 (for example), you will make or lose that amount multiplied by your "Quantity" or stake size.
That market movement is also called "points" or sometimes "pips".
Confused? Let's use an example...