It is so exciting for children and adults to start seeds early inside. A sunny south facing window sill will do. A seed heating pad to keep soil warm can be used, as most seeds require a warm soil to germinate. Lights can provide a longer day which will keep seedlings from growing long and floppy. While this equipment is not absolutely necessary, it does promote good results.
Read the seed packet. It has some useful information. Often the seed packet will tell you when to start the seed inside for an early crop. It may say something like “start indoors 4-6 weeks before last frost”. If you don’t know when the ‘last frost’ is likely to occur, contact your county extension agent, or local nurseryman, or garden club. You could also google your location's last frost date. Then find that date on the calendar and count back 4-6 weeks. That is when it is appropriate for you to plant your seeds inside. If your seed packet lacks information, contact the seed company.
Choose a container. Small seed, such as lettuce, may be started in a seed tray and thinned out to two or three seedlings per cell. Or a shallow pot can be used. These seedlings can be gently separated and replanted in a cell tray and grown until they fill the cell, then moved to the garden. Larger seed, such as peas, can be planted individually in a 3 or 4 inch pot.
Use a seed starting soil mix, especially for small seeds which are planted quite shallow, perhaps a quarter of an inch deep. This specially prepared soil is fine enough to keep seeds moist, yet well drained to discourage fungus from growing which can kill seedlings. Larger seed may be potted in a regular potting mix and an inch deep. A good soil mix will have a wetting agent which makes is easy to soak the soil thoroughly before planting. If your soil mix has dried out it will take some time to wet it thoroughly. When planting small seeds, I make sure the soil mix is wet, sprinkle seed on top and cover lightly with dry soil, then mist well to keep seeds moist.
Next set the tray/pot in the window. Cover with a plastic wrap until you see the sprouts. Uncover and watch the seedlings grow. When the seedling has at least four leaves you may fertilize LIGHTLY.