Confused about to-do lists in mac mail

Hello all, I am slightly confused about the different to do lists that I have in mail. I have tried to use the help section and also google but can't seem to find what I am looking for.

In mail I have 4 different to do lists - "on my mac", ".mac", "1xxx@mydomain.com" and "2xxx@mydomain.com"

Then on my iphone my @me.com address has an apple mail to do folder and my other 2 addresses that correspond to the 2 @mydomain.com addressses above also have an apple mail to do folder.

I then have a to do list on the me.com website.

My question is what is the difference between all the to do lists in mail?
What is the diffence between "on my mac" and ".mac" and do the to do lists that are specific email addresses then sync with the folders on my iphone?
What is the relationship between to do's in mail and ical? Can you create in both and have them show up in both?

Ok that is more than one question

As ever, any help is very much appreciated as I am trying to get more organised

 

anyone have any ideas?