How to copy & paste text from emacs documentation?

I am writing my own emacs cheat sheet. So I want to copy function descriptions from emacs help.

For example, in this screen shot, I want to copy the "org-shifttab" function description: The "pattern" field filters a list of functions. Pressing TAB displays the description of the selected function. But moving the yellow cursor out of the "pattern" field removes the display of the function's description.

How to copy the function's description to the clipboard?

I am running Emacs 25.2.1 on Fedora 25.

You have a *Help* buffer now with the contents that you're looking for. You can either press enter to go to that help buffer, or use C-x b to switch to it.

From there, you can mark and copy the contents of the buffer as usual (C-x h M-w).