How can I try the new compose experience?
You may notice that the new experience appears for your automatically. If it doesn't but you want to try it out, just click the Compose button, as you normally would. Then click the “new compose experience” link at the top of the message.
I can't find some of the text formatting options.
To help you focus on your message, Gmail doesn't show you all formatting and content options until you need them. For example, to see all the text formatting options, you need to click the format icon, as shown below. You can also choose many options using new keyboard shortcuts.
For details, see what's different about the new Gmail compose experience.
Can I switch back to the old compose experience afterwards?
As of August 27, 2013, you cannot switch back to old compose.
Will the new experience eventually become permanent?
Yes. The new experience is permanent.
I can't find any option to try the new compose experience.
Your domain administrator has likely opted out of showing
new features as soon as they're released. In that case, you won't be able to try the new experience quite yet but you should see the option for trying it very soon!
You also won't be able to try the new compose experience if you're using Internet Explorer 8.