In the list view you can see the available breakpoints:

In the edit view the only mandatory field is the breakpoint in pixels. Here you should enter the width of the container upon which the slider will change it's behavior. You can also completely disable the slider by checking the checkbox next to the breakpoint field. Please note that it will not re-initialize the slider if you resize the window again.

If you would like to change a setting then you first need to check the Override box. Then the desired field becomes editable and you can change its value.