Genesis 1 is a synopsis of creation. In the beginning God created the heavens and the earth. That's why throughout Genesis God details the parts of creation that came to be created.
Genesis ch 1 is a record of the order of Creation. Verse 1 has no timeframe connected to the following account of the earth’s preparation for habitation. So this event could have been millions or even billions of years before preparation began. The earth itself is very ancient. It is mankind alone that are the most recent residents. Our history dates back only 6,000 years. Many animals were extinct by the time God created humans.....so this also reinforces the fact that the Genesis “days” were not only 24 hours, but undetermined periods of time. The Hebrew word for “day” allows a variety of meanings, not just a 24 hour period.
The first “living” things stated in the Genesis account were vegetation of various types and would include all the different types of greenery that would serve as food and even habitats for the creatures that were to follow....grass, plants and trees. God prepared this in advance for them.
It would also include microorganisms in abundance which would have been present in the soil to aid the growth of trees and plants, as well as the breakdown of dead vegetation to add fertiliser for future growth. Enough light from the sun would facilitate photosynthesis. “Light” was there from the beginning because the Universe was created as a whole. The sun was there in our solar system, but was not visible from an earthly point of view until day 4. Until then, the earth was “swaddled” or completely covered with clouds. (as Job 38:9 points out)
The account does not go into detail, but we have the science of agriculture and other scripture to fill in those blanks.
