فقضاهن سبع سماوات في يومين
Then He completed and finished their creation (as) seven heavens in two Days.
means, He finished forming them as seven heavens in two more days, which were Thursday and Friday.
وأوحى في كل سماء أمرها
and He decreed in each heaven its affair.
means, He placed in each heaven whatever it needs of angels and things which are known only unto Him.
وزينا السماء الدنيا بمصابيح
And We adorned the nearest (lowest) heaven with lamps,
means, the stars and planets which shine on the people of the earth.
وحفظا
as well as to guard.
means, as protection against the Shayatin, lest they listen to the angels on high.
ذلك تقدير العزيز العليم
Such is the Decree of Him, the Almighty, the All-Knower.
means, the Almighty Who has subjugated all things to His control, the All-Knower Who knows all the movements of His creatures