RE: What's the meaning of "^A" in emacs?

[Drew Adams]

> What't the meaning of "^-characters" such as ^A, ^_, ^O ? I see this
> characters in some files. And How can I input this characters?

See the Emacs manual, node `Text Display'.
http://www.gnu.org/software/emacs/manual/html_node/emacs/Text-Display.html

You can insert any control character by first hitting `C-q' and then
hitting the character (e.g. use "Control + q Control + a" to insert
the Control A character.

For info about `C-q', see the Emacs manual, node `Inserting Text'.
http://www.gnu.org/software/emacs/manual/html_node/emacs/Inserting-Text.html