Genèse 3:21

And the Lord God made to Adam and to his wife vestures of honour from the skin of the serpent, which he had cast from him, upon the skin of their flesh, instead of that adornment which had been cast away; and He clothed them.

כתנות עור וילבישם, coats, long enough to cover the whole body.

ויעש ...כתנות עור, without any input by man, similar to a description of the Talmud of what the earth will produce without human input in idyllic times when ready made bread rolls will be produced by the earth (Shabbat 30)

וילבישם, in order that He would not have to expel them from Gan Eden while they were naked. Not only that, but if they would dress themselves in these coats after having been expelled, they might delude themselves that they had improved on G’d’s handiwork.

ויעש ה' אלוקים לאדם ולאשתו כתנות עור, seeing that they had been naked, but had made themselves the aprons made from fig leaves, to cover only their genitals, G’d now provided them with protective clothing for their entire bodies, probably also having in mind different climatic conditions outside the garden. ולבישם, “He dressed them in those coats. There is no point in asking how G’d made these coats. Surely, by comparison to the entire universe which G’d had created, making leather coats was a very insignificant accomplishment by comparison.
When we find a sage saying in the Midrash (Torah Shleymah by Rabbi Menachem Kasher items 176,and 186 on our chapter) that these garments were made of skin, i.e. that man had consisted of bones and flesh without an outer layer of skin. G’d now provided the skin as a protective cover. (attributed to Pirkey de Rabbi Eliezer chapter 20) [the Talmud Niddah 25, discussing when an aborted fetus is to be treated as a human being in some respects, states hat the fetus is not covered with a skin until it is fully formed inside the mother’s womb. Ed.] We do not understand how this solves any problem at all. They would have been worse off than before, even their genitals having remained exposed, as these too are covered by skin. Some scholars claim that the skin was skin of the serpent which G’d had removed from it and clothed Adam and Chavah in it. Yet other scholars claim that G’d commanded one or two of the larger mammals to remove their skin, and that Adam and Chavah then proceeded to dress themselves in those skins.
There is no need for all these fancy explanations, i.e. speculations. G’d simply issued a directive and the tunics came into existence, just as the material from which the first set of Tablets was made by G’d had to come into existence by miraculous means. Our sages (Sotah 14) record the opinions of the great scholars Rav and Shmuel, the former saying that the meaning of כתנות עור is “coats, tunics, made from material removed from skins.” Shmuel said it refers to raw material from which the skin (man’s) derives pleasure. To be specific, it refers to cotton. Our sages also say (Midrash hagadol on this verse) that these garments belonged to the things that were created in the twilight zone of the 6th day of creation, immediately before the onset of the Sabbath. Rabbi Simlai (Sotah) uses the opportunity to tell us that the Torah commenced with acts of personal kindness by G’d for His creatures, and ends in the same vein. Here, in Bereshit, we are told about G’d, personally, providing clothing for Adam and Chavah, whereas at the end of the Torah we read of G’d, personally, burying Moses. (Deut. 34,6)