A Push will send data from your design to your spreadsheet and create new sheets and keys.
One of the easiest ways to get your spreadsheet up and running quickly with a design is with the Push. Pushing content can also be helpful when you want to make content updates from within your design file.
To push content, select the layers you want to push and press Push > Push Content. This will update the selected content version and only the layers that are selected.
ContentSync does allows designs to be pushed to the ContentSync platform for additional features however this is not supported in Adobe XD at the moment.