Streetcomplete can only add data to objects that are already mapped.
You can't really create new objects using this editor

I have mapped a few buildings in an area where you created lots of notes. New Streetcomplete quests should show up within a few minutes :)

Notes that are created using Streetcomplete are public and visible for everyone. Which means sometimes people solve them before you yourself get to it 

But let me know if you need help getting started with editing Openstreetmap on the computer

PS:
press comment, if you only want to add a comment
Press comment and resolve, if the the note no longer serves a purpose (for example, someone has mapped the requested changes)