The furthest right column is for final calculations, and you move in left as you need to do workings. If you look at marking schemes you will understand. I didn't know where all the calculations went when I first started, but once you do a load of them, it will come natural.
To build up on what K_684 said:
In the first column, you have your details which you know (obviously).
In the second column, you have figures here if there is more than 1 Purchase and a less expense with adjustments (like light and heat prepaid or light and heat due).
In the third column, if you have figures in the second column, your final answer for them will go here. Less expenses also go here as well as the final answer to a less expense with an adjustment. If sales has returns also, you put sales and sales returns into this column too.
In the fourth column which is the final column or third small column, your final answers / calculations go here. If you're adding reserves at the end, you put them also into this column.
And like what he said ^, once you do more and more, it will become very easy and you will know how to do them just like that (FINGER SNAP).