It may be oversimplifying things to say that , in Zen, the source of everything is nothing. Nothing is a term that seems easily understandable. It may cause confusion if a simple, understandable word attempts to describe that which cannot be described. However, there is great value in confusion. When we cling to what we know, we can lead ourselves deeper into our delusions and ignorance.
There is no hope of avoiding confusion, delusion, ignorance in new or old Zen practitioners. Raising confusion and exploring delusion is a big part of practice. Those who experience that great unknowable, source, unconsciousness, report how unsubstantial all of their knowledge is. Confusion is a good place to start when seeking to know what you cannot know.
Nothing is as simple as it appears. Nothing is a self contradictory word. Depending on your interpretation, the first sentence in this paragraph can mean two very different things. There are many good words like nothing, which point out form and emptiness in one entity. The Source everything, is more like no-thing, un-conscious, un-substantial, con-fusion, un-knowable, in-describable, non-entity.