Hi,
When you open a screen the input field with ‘auto-focus’ will automatically be selected and the keyboard pulled up, so you immediately can start typing.
This only works in native builds though. Not PWA.
Btw: if you apply ‘auto-focus’ to multiple fields on the same screen the last one will be selected, as I found out a few days ago 
Recommend just turning auto-focus on for one input field per screen.
Best,
Steven