I was trying to mark an email as "Important" in Gmail and accidentally archived it.
Now I cannot locate it, since there is no "archive" label anywhere.
How do I get it back?
Click on All Mail on the left. When you see the message, open it, and choose the Move to Inbox option to "un-archive" it.
Alternatively, you can use the search feature to locate the message (the search box should be towards the top of the Gmail page).
For more details visit Gmail Help.