A seed becomes a plant by planting it in healthy soil, giving it lots of water (but not to much) and sunlight. Shortly after time, roots begin to develope and the seed germinates. After a week or to the seed has sprouted and the plant has become matured.
As seed becomes a new plant by photosynthesis and taking in sunlight and water. That is how the seed develops into a plant
I have started many new plants in my apt. By placing seeds deep in the earth, giving them a lot of light and water. I have two avocato trees growing in my apartment, them I just drop in the soil, half immersed, and lots of sun.