How to create a select box field to select from a filtered list of articles? in this example, I want to make the select box to select from a filtered list of articles. 

What is the proper way to customize the options available in this select box ?
Step 1

To have such a list of articles that can be referenced, you should first (repeat: first) create a view (with the Views module) to create a list of all the articles that are allowed to be selected. And the display type of such view must be an Entity Reference display.

Step 2

Your select box field (to select from a filtered list of articles) should be field that looks like so:


Field Name = Anything you want, eg field_articles_list.
Field Type = Entity Reference, using these additional settings for it:


Target type = node
Number of values = 1 (probably, though something like "unlimited may do as well).
"Mode" (within "entity selection") = Views: Filter by an entity reference view. However, before you can select an appropriate view at this point (which is eligible to do so), you first need to create a view with an Entity Reference display, or add such a display to an existing view. In your case, you should select the view created in "Step 1".
Pick any of the other options to define this field as you see fit.