Push notifications are enabled by default as part of the iOS device. All you need to do is choose which apps you want to get notifications from and what type of alerts they send.
Here's how to do that:
Tap the Settings app to open it
On this screen, you'll see all the apps installed on your phone that support push. Settings for each app are managed separately, so find an app you want to configure and tap it. Tap on LeadOwl.
The first option is to Allow Notifications from this app. If you want notifications, move the slider to On/green. If not, move it to Off/white and go on to another app.
To enable Sounds so you receive sounds for pushes and notifications move the slider to On/green.
Be sure that you're on the newest version of LeadOwl by updating the app regularly when you get the prompt to do so.