Meaning of 道生一,一生二,二生三,三生万物
The meaning I would present is


  With the principles of nature, the fundamentals were produced. Everything else are then produced from the fundamentals.


The explanation of the principle and the fundamentals differs from people to people, it depends on your belief, the major you study and other backgrounds.

I, as a physics student, would regard the principle as the physics rules and the fundamentals as particles that make up the universe.