Hello,
I really don't understand your question since I already gave you all the elements before.
As I wrote, the button is just one little thing.
Adding a button is quite simple, but that button is doing an action ; which means that it requires some code to perform that action (adding a product with all its settings into a cart ; not just move it).
It does not matter where that button is or how it looks like ; the final action is still the same ; the code behind it is still required and is still what is complicated.
Regards,