Hey there,

I am really sorry for the delay of this reply as it is a weekend for us here.

#1. Save for later - It will save as draft post first.

#2. Apply - It will publish the post directly. At the same time, the system will ask continue edit the post or redirect to post listing page.

#3. Update post - when you edit the post, it will show this `Update post` button and this button purpose similar with save.

Hope this help.