Adding onto Chris's answer, elaborating more into the fine detail, here is kind of a step process of how it all works

1. you have local task/form to work on. you log out from the app.

2. fill out/complete your task/form and hit the submit.

3. your task/form will now be in the outbox of your local Forms

4. Log back into the LF App, and into the same respective Forms server as the local Form/task you submitted, and as the relevant user. 

5. the Form/task(s) will then automatically upload and submit into your Forms Server.

Note: What is meant by "connectivity is restored", is when you log back into the Forms Server via the mobile app as the respective user into the respective Forms server. So it's not a scenario where you just need to connect back to your phone network or wifi and you are good to go. You will need to log back into the Forms server from the LF App. 

So is the only way to get this functionality to work to log out of the app and use offline mode when you don't have connectivity?  One would assume this would all be automatic, but my testing on iOS seems to indicate that if I lose connectivity (turn on airplane mode) and fill out a form, it goes into my outbox and is NOT automatically uploaded at any point (either once connectivity is restored, or logging out/in, in/out).  This is a big challenge for us.  My users shouldn't have to log out when they don't have connectivity, the app should deal with that automatically.  I will also note that when using airplane mode, after a form is submitted,  I get a screen saying, "The form will be uploaded when a connection is established."

- Alon