You will see this view (offering the option to mark your ePoster as ready) when you have closed the stack/ePoster editor.
You need to click on both buttons to indicate that it is ready to print and ready to publish. In fact there will be no printing done for online only conferences, but you still need to click the ready for printing button. In future this button will be removed for online only conferences.
We strongly recommend that you preview your stack/ePoster and check that it works as you expect, before you mark it as ready to publish.
Marking your stack/ePoster will let the administrators know that your stack is ready. It will not be published to the showcase immediately, as the administrators will take that action and they may have many stacks/ePosters to review. However, once it has been published then you will see a message onscreen indicating that this has been done (as shown in the image below).
If you do not see the buttons that allow you to mark you ePoster as ready then this will be because you are creating a stack/ePoster that is not linked to a conference/event invite with a showcase. In this case you can instead make your ePoster public yourself by changing its access permissions.