Thanks for the question.
The phrase relates to the principle, the source, and the efficient cause of the whole creation. When studying the Greek you can see the causal attribute in its preeminence, and the related words from Strong's dictionary below:
|746. ἀρχή archē, ar-khay´; from 756; (prop. abstr.) a commencement, or (concr.) chief (in various applications of order, time, place or rank): — beginning, corner, (at the, the) first (estate), magistrate, power, principality, principle, rule.
The idea is that God spoke His Word, the Word, the Logos, and all of creation came forth. We understand that Jesus Christ is the Logos (cf. John 1) and is the very means by which God issued forth creation.
The confusion comes from heretics like the Jehovah's Witnesses that suggest that Christ is not the unbegotten Son of God but rather the first of created things himself.
A good reading of the first chapter of John's Gospel will dispel that notion, in addition to the many places in Revelation (Revelation 1:8, Revelation 21:6, Revelation 22:13) where He is the Alpha and Omega—the Beginning and End, a reference to the eternal nature of God.