How to: function template_main_left

[nightware]

I'd like to modify the basic layout from

Code Select Expand


|      HEADER       |
-------------------
|     CONTENS      |
-------------------
|      FOOTER       |


to

Code Select Expand


|      HEADER       |
-------------------
|MENU| CONTENS |
-------------------
|      FOOTER       |



I want the MENU part to be a list of links, but that has nothing to do with my question.

i have tried to figure out how to do it, and I started out by writing a function:

function template_main_left

It seemed like the right way to do it, but I cannot figure out where to call it from.

Please help.