The Qur'an says: All His command, when He wills something, is to say to it “Be,” and it is. So glory be to Him in Whose hand is the kingdom of all things and to Whom you shall be brought back (36:82-83).
The clause "all things" in verse 36:83 includes any essence, quality, action or effect. Their command (amr) which is in the hands of God, is the word "be" (kun) which indicates giving existence to an entity. God's command is the existence that He bestows upon all things, by which they come into existence. When He says to something, “be,” it becomes.
This bestowed existence is connected to God on one end, and in this sense it is called “God’s amr (command),” which is the divine word, “be.” It is also connected to the being which is given existence, and thus it can be ascribed to the being as “its amr,” which again is the aspect of the being that traces back to God. This aspect is referred to as “and it is” (fa-yakūnu) in verse 36:82.
To summarize: God’s amr (command) means giving existence instantaneously. It includes the existence which He gives to an entity in the first place, as well as the existence that He gives to its qualities and effects. God is in charge of not only the very essence of every being, but also how every being is structured and functions.
God’s khalq (creation) means giving existence according to some measurement and composition. There are verses that show that God's khalq (creation) includes and applies to everything. God says: and He created everything and determined it in a precise measure (25:2).
In other words, khalq means giving existence to something according to some plan, measure and order, whether that thing can be differentiated into separate parts (as in the case of compound material beings) or not (as in the case of simple immaterial beings). This is contrary to amr, which is giving existence without the aspect of measurement.
The Qur’an shows two subtle differences in the usages of the words khalq and amr:
(1) Khalq is sometimes gradual, as the Qur’an says: Who created the heavens and the earth in six days (7:54). However, amr is not gradual as the Qur'an says: And Our command is but a single (word), like the twinkling of an eye (54:50).
(2) Khalq is sometimes attributed to other beings than God, as He says (addressing Prophet Jesus): when you would create from clay the form of a bird, with My leave, and you would breathe into it (5:110); and He also says: So blessed is Allah, the best of creators (23:14). However, amr, in this sense (of bringing something to existence) is never attributed to other beings, but is reserved exclusively for God.
In short, khalq (creation) and amr (command) are two considerations of the same essential meaning of bringing something to existence. Khalq is a stage of creation which is subsequent to some measurement. Therefore, it best applies to the creation of the very essence of the beings, because the process of giving existence to an essence involves the determination of its features and effects. Amr, on the other hand, best applies to the creation and management of the features and effects of the beings, and the general system of causes and effects through which they interact with one another, all of which is subsequent to the creation of their essences. This distinction is applicable when both terms are used together. Otherwise, if they are used independently, each term may be used for all stages of existence, whether it involves measurement or not.
Reference: Al-Mizan English Volume 15, pp. 224-229, first edition, Tawheed Institute Australia Ltd., 2018