Task that works on 2 indepent lists

Does anybody know how to create a task which works on 2 independent lists. 

Let’s say I have a list with demands and I have a list with supply’s. These 2 lists are shown on 1 screen and horizontally devided. (I’ve created a reference with no reference columns) So the top list is the demand list and the below list is the supply list.
I want to be able to select a demand line in the demand list and to select a specific supply line in the supply list as well.
Then I want to start a task which can connect this specific demand line and this specific supply line. For example to create a new orderline based on this selected demand line and selected supply line.

An example is the task “create list bar item” in the SF. In that case the system knows which subject I want to add to the listbar and the system knows as well which menu item (at the left side) is selected so the chosen subject will be placed in the correct submenu. Can we do this with two independent lists as well?