Once Hour of Devastation begins to resolve, no player may take actions until it’s done. Notably, players can’t try to give a creature indestructible again to save it from the damage.

Creatures with indestructible that enter the battlefield after Hour of Devastation resolves will still have indestructible.

There are many important moments in the story, but the most crucial—called “story spotlights”—are shown on cards. These cards have the Planeswalker symbol in their text box; this symbol has no effect on gameplay. You can read more about these events in the official Magic fiction at http://www.mtgstory.com.