Customers who use an app for the first time should spend their first 30 seconds enjoying the app and seeing what it has to offer. You don't want customers to spend the first seconds of their app struggling to figure out how to use it. A great way to get customers started is by implementing a couple of intro slides that explain how to use the more complicated or less intuitive features of the app.
These slides shouldn't be mandatory to flip through, and should have an exit option at anytime if customers just want to dig in on their own.
There are plenty of times where a customer might want guidance after initially opening the app therefore it is important to make these slides available to be viewed at anytime.