Re: The ad-supported app
In Android, find the setting app. Go to the notification section. Find App notification and click on it.
Click on each app that you do not want notification and deselect show notification (it should be a very long list and it should take some time without another app to automatic do it for you). This procedure should be very similar to iphone.
For other android device, it might be under installed apps. Click on the apps to find the app details. Find the option for turning off notification and click on it. (repeat for all unwanted notification)
If for some reasons there are still notifications you did not asked for (after deselected) or the option just doesn't exist, then your android might be too old and will need to install a push notification blocker.