How to save user editable text field?

I want to have a text field on one page where anyone can write anything they want and then save it. Latest save will overwrite the previous one. I also want to display this text on other page. I would guess it has to be a template variable? And I could call it with Ditto, but I have absolutely no clue where to start with the text field (or even TinyMCE field?) and how to save that when use presses the save button.

Cheers,
Tommy

Exactly, you need a Template Variable.

1) Go to Elements > Manage Elements > Template Variables > New Template Variable

2) Add these parameters:
Template Variable Name: customContent
Caption: Enter the content here
Input Type: text (Note: if you choose RichText you can edit the content with TinyMCE)
Default Value: @INHERIT
Template Access: Choose the template where you want to show the content

3) Add [*customContent*] on your template or in a Chunk. If it doesn’t work try with [+customContent+].

Be aware that @INHERIT will work only if you input the content from a parent page:
"@INHERIT - inherits the value of the same TV as set for a parent document."

There is also another way, if the first doesn’t work. Try to follow this tutorial http://wiki.modxcms.com/index.php/Use_a_Document_to_form_sidebar_content