Genesis 2:19-20: “Out of the ground the Lord God formed every beast of the field and every bird of the air, and brought them to Adam to see what he would call them. And whatever Adam called each living creature, that was its name. So Adam gave names to all cattle, to the birds of the air, and to every beast of the field. But for Adam there was not found a helper comparable to him.”
Today there are millions of species of animals, but a species has multiple definitions. When talking about creation, we use the word “kind,” which is closer to the “family” in the standard classification system. Take the canine kind for example: There are wolves, dingoes, coyotes, domestic dogs, and foxes. Then, from each of these species comes a plethora of even more species (Retrievers, Poodles, Terriers, etc.). The scripture above implies that Adam named the animals in a short time, and its possible it happened in one day. He named the animals but was unable to find an appropriate help mate. God then put Adam to sleep and formed Eve, his wife, from Adam’s side. While naming them, he was trying to also find a helper.
Skeptics claim that Adam could not have named the millions of animals in existence, much less remember them all. To answer this claim, we must consider two things. Adam was the first human, and although he later sinned, he still had near perfect genetics and minimal effects from the curse. Therefore, Adam’s memory was much more intact and detailed because it was not affected by thousands of years of curse, like us today. Second, most likely Adam named only the kinds of animals God had created. God commanded the animals to reproduce after their kind. But, with there being only a short time frame from the creation to the command for Adam to name the animals, there would not have been any offspring from the created kinds yet. Therefore, the animals did not speculate from their kind. Only the representative kinds would have been available for Adam to name.
In the past, creationists have claimed that Noah, who had taken each of the representative kinds of animals on the ark, may have had as many as 16,000 kinds on board. Lately, however, through the research being done for the preparation of the Ark Encounter Project, estimates of the kinds has greatly reduced to less than 1,000 kinds/families. See this article for more information about creation taxonomy, also known as baraminology.