What does selecting sync for a folder mean?

Im using nextcloud 20180622 on android 6.0.1 with nextcloud 13.0.2RC1.

When I press the ellipses when viewing all files, there’s an option called sync for folders. It dutifully makes a copy of the server’s files locally. I have sync enabled in settings, account, nextcloud.

Does this mean:
Changes on the server will appear locally in the future without any further intervention?
When should they appear?

The nextcloud repo is /storage/emulated/0/Android/media/…etc…/cloudrootfileshere
If a folder that has been selected with sync as described, is a local (mobile client) addition to that file name space supposed to at some time in the future appear on the server?
When should it appear?

I’m not seeing local files ever appear on the server in a folder I signed to sync, but before going further, is it currently supposed to sync the new file to the server?