again, this is accomplished using a template variable.
first of all, if your left column is your main content, then you should use [*content*] there. all document-specific template variables are listed here:
http://modxcms.com/document-tvs.html
if you do not use [*content*] somewhere in your template, you’re basically cutting yourself off of many of the features of MODx and undermining its functionality.
so, let’s say your left column content is your main content. as i said before, use [*content*] there, as that variable will be populated with the HTML code you use in the "Document Content" for each page on the back end of MODx.
then you would need to create a template variable that functions just like [*content*]. the only difference is that it is customized by you, and not part of the core of document-specific variables. it works exactly the same way, though.
so, on the backend, go to Resources -> Manage Resources, then click the "Template Variables" tab. select "New Template Variable" and give it an appropriate name like "rightColContent". give it a caption and description. if you would like a blank text area to paste in raw HTML content on a page-by-page basis, select "textarea" or "richtext" as the input type. if you have default right-column content you’d like to include, paste it in "default value".
(perhaps you only have three or four different "chunks" of right-column content that you want to use interchangeably on your site. in other words, pages in one area of your site will have the exact same right-column content, while pages in another area will have different content, even though within that area it’s all the same. in this case, i would recommend making each area’s right column content a separate chunk, and then set up your template variable to select these chunks on a page-by-page basis with a dropdown box or radio buttons. that way if you want to change the right-column content for just one area, you would only need to change the chunk as opposed to every single page within that area.)
finally, assign the template variable to the template you’re using. then edit the template, and where your right-column content should be, include the [*rightColContent*] call. edit any page in your site and scroll down beneath the "Document Content" area to see your "rightColContent" textarea for inputting right column content.
this is a very simplified way of doing what you’re asking. please make sure you read over the
tutorial on creating template variables to fully understand the functionality and power of tv’s.