I am definitely no programmer, but I'm guessing you looked in the general html file for the theme, and seen where they had a top section, and a bottom section with the $content between them. This is pulling from the core, and loads all of the site content, and I'm guessing the left, and right sections. I don't know where all of that code is specifically located. Looking through some of the files there are several files related to content, and sections, but what each does is way beyond me. If you are referring to adding the sidebar component, that isn't done by modifying core files. That is done by adding the component to the general, and dnd index html files for the theme along with the css to support the sidebar. I referenced the files from themes that had the sidebar to successfully add it to my themes.

Firstly thanks for replying as I did make a thread earlier too.

I am working on a theme and want to add another column on some pages like main.
I have looked through the core and found the functions which do the background work but the content like the page layout is location somewhere else (i think in .html files).

So how could i get access to $content file/folder ?

I have another question since you design themes. Is it possible to user the default 'Simplicity' theme for the base and modifiy that to create new themes and add them to the store.
I don't know if I am allowed to make and sell themes like that.

Thanks you.

I don't know of anyone physically adding an additional column. The design is limited to the core. There are a few themes in the store that have managed to split the newsfeed into two columns; most likely through css sizing elements. If you were able to find the core files, and changed them. The next platform update would wipe your changes out.

You can use the base free themes to design, but they have to be your own design. This meaning it can't be just a simple color change, and stick it in the store to sell. I could have sold my themes because they have heavy modifications in design, and functionality, but I am not a pro theme designer. I did them to see if I could, and learned a good bit about css in the process.

Okay, Thanks for the help. I will take a look at some themes which have managed to do this.
You can have a look at my theme here: http://vmclan-ac.tk (not 24/7 hosted server, so the website might not be online when you are viewing).