Setting Destination with Mouse Down

PLEASE EXCUSE MY NOOBIENESS...
I am really struggling in how to grasp using a mouseDown event to determine the destination of my object.



So far my idea is...

function setCubeDestination::onMouseDown(%this, %worldPos, %clicks)
{
///my first line of code must set or record the position of the mouse when clicked but I am unsure how as setPosition is for an object, not a mouse click, but can a mouse click be an object?

///my second line must determine that this record of the mouse clicked position, is the destination for the object. setPositionTarget?


///my third line of code must tell the object to move there at said speed, using X animation. moveTo? animation can come later
}

I am very confused, mainly because the methods I want or think I should use, appear as functions to me with their own variables, and as such I am unsure of how to implement what I think should be pretty simple for anyone with relatively good experience. Please help a newb.