Update custom column's content?

I'm a perfect rookie coding on phyton (and even more coding for Calibre).

So I began first looking at some plugins and trying to modify and fit it to my requirement.

I'm trying to upload some columns from a list and updating whith its contents some custom columns at Calibre library.

Now, I'm able to load the contents from the file into a colection (I look at code from some plugins to understand how to do it). But I don't know how I can do to update the content from a custom Calibre's column whith my data.

Can somebody give me some tricks for it? The easiest way, please, remember I'm a rookie...