This varies from broker to broker. The market norm is $25 per trade but we also have brokers which let you do $5, $15 and $25 minimum amount trades. You can see the minimum trade amounts in the Brokers Tab. You don’t have to always use the same trade amounts you can place higher amount if you are confident that your prediction will be correct.
The slider shows the Trade Amount where you can adjust your trading amount to adjust your risk level.