Creating items in online vs up

[scarletreagan]

Can I create a new item in the online platform vs the square app or do I have to do both to have it in my inventory?  It seems even if I am duplicating an item I still need to go into UP to add stock to the item and UP doesn't let me do everything to get it online. 

There also seems to be a lag of when I am creating an item online for it to show in the up platform.  Looking for most efficient order to get in both platforms.

Also how to I get thumbnail photos to show up in online items....