First, make sure you have Push Notifications activated in the Settings section of the app.
Now, to set up a price alert, go to the contract for which you need to set it. Click on the "(!) -Set Price Alert" icon in the menu.
Select the Price at which you want to be alerted, and optionally, the expiration date and alert text. Once you set it, it will appear in the "Alerts" section in the main screen.
When the condition is met, you will receive a Push notification alerting you about it, even if the app is closed.