How to navigate between pages

Well I have some registers pages, I want to save the page that the user is in, for example, the user register the phone number, then he has to complete the register with email, and password in page 2, but if he gets a call or close the app, I want to open where he left, if is complete almost the form, then open in page 2, not in the init of the app.

How can I do that?

Do you have any code that you can share?
What have you tried so far?