how do you put an item in the set box(the one that says empty on it if you saw them in the market) and how do i get sell the full chronos or whatever

You must have the set item. You can buy it here: http://forum.toribash.com/tori_shop_item.php?id=1458
go to your inventory and check the box right next to the item you want to put in to the set.
At the top, find "With Selected" then click the drop down button. There should be something that says "Add to set: <setname>". Select it and click submit.

To get full sets, you need to buy all of the items of that color. You can see the color's items here: http://forum.toribash.com/tori_groups.php

ok thanks