If you live in an area with a short growing season, you need to start many vegetable and flower seeds indoors. Peat pots, purchased at nurseries and garden centers, are convenient for starting seeds, but you really need nothing more than plastic sandwich bags.
Fill each sandwich bag halfway with potting soil purchased from your local garden center. Press the sandwich bag onto a tray so that the bottom of the bag is flat and will remain stationary.
Follow the seed package directions on how deep your seed should be planted. Insert the seed and cover it with soil.
Moisten the soil by misting it with a water bottle.
Fold the bag's flap over the top to keep the seeds warm enough to germinate. Do not seal the bag--air should still be able to get inside. If you are using resealable bags, leave 1/4 of the top unsealed. Place your seed tray in a sunny window or under grow lights.
Mist your seedlings as needed. The soil should not be allowed to dry out. However, do not water so much that the soil is saturated.
After your seeds germinate, transplant the seedlings into the garden when there is no longer a threat of frost.