The onboarding process is a journey your users have to go through from the moment they sign up, until they reach the "Aha!" or "Wow! moment". Unless you will be able to guide users to their desired outcome, there's a very slim chance any of them will return in the long-term.
Here are 21 resources that will help you gain a better understanding about user onboarding and everything that's involved into providing a great first-time experience for your customers: