If you keep seed, it should be stored in a refrigerator. Use an artificial mix-not soil. Many of the commercial type mixes are now available for homeowners. I tell people to pick up a bag of potting soil in the store-if it feels very light, it is probably a good potting soil. Many potting soils include a starter fertilizer solution.
Organic gardeners can use screened compost as a medium if it is well composted.
I like to use vermiculite to cover them. A few seeds, such as lettuce, need light to germinate so should be barely covered. There are some seed mats and other systems available to warm soil. The greenhouse or environment above the seed tray can be surprisingly cool as long as the soil is warm. Seedlings need light-if grown in a house, they should be moved outside on warm days.