Cotyledon (or "seed leaf") is the first growth to appear upon germination, it is really the embryo within the seed of the plant.
It is appropriate when seeing "seed leaves" to do a small victory dance! You have your 1st success!
Light now becomes a requirement, place florescent grow lights as close to the seedling as possible, provide at least 14 hours of light daily. Secondary or "true leaves" should emerge within 7 to 10 days. Monitor the growth and move the light up as needed.
Moisture levels most also be monitored, damp not wet potting media is required. Also bottom water and never allow the tray to sit in a pool of water.
Once several sets of "true leaves" have grown and girth is achieved in the stem, begin watering with a very diluted fertilizer. 20:1 ratio.
to be continued.....