Apple lets certain apps integrate with Siri in iOS 10, which means you can say things like "send a WhatsApp message to John" or "get me an Uber."

The catch is that not all apps can work with Siri yet, namely Apple Music competitors like Spotify. 

Here are the types of apps that can work with Siri:

Ride hailing (Uber, Lyft, etc.)

Messaging and photo search Payments (Venmo, Square Cash, etc.)

Voice calling (Skype, WhatsApp, etc.)

Health and fitness (Nike+, etc.)