Version history is the safety net under a Copilot Page. A Page is a persistent document that you and colleagues edit directly or extend by chatting with Copilot, so changes pile up. Version history keeps the earlier saved states. You step back through them with the arrow in the upper-right corner of the Page, then choose Restore version to go back or Cancel to stay where you are.
It is useful for more than fixing mistakes. When a colleague reworks a shared Page, the history shows what it looked like before, much like Word's own version history. That beats rebuilding a lost paragraph from memory, or pasting copies into Word just in case.