http://www.burpee.com/ This site has 'how to' videos and has information about which flowers need full sun, which need shade and stuff like that. It is simpler to buy flowers that have already been started and you just transplant into the ground but growing from seed is cheaper although more work and may require plant lights if you don't have enough windows with good sun exposure.

Marigolds are easy to grow and if you put them in with your vegetable garden the marigolds will repel insects.