I would like to start planting flowers because I absolutely LOVE them. The only problem is that I know almost nothing about planting flowers. I can very easily find out how to plant flowers (how far in the ground/ how far apart) so I don't really need that kind of advice. I just don't know what kind of flowers to plant!
I'm a highschool student so I don't have that much time or money to spend on flowers but I do have sufficient time and money to spend on them. I live in Kansas so I have average weather... decent snow in the winter, and jacket worthy springs and falls. When should I buy and plant the flowers? Also, what are good flowers to buy following the previous criteria? I live in an open fenced neighborhood so I can't have flowers that spread extremely easily but I'd prefer to have ones that return each year (are those called perennials?). Last question: where to buy them? All help is appreciated. Thank you!

Since you are new to gardening then you should start off with flowers that are guaranteed to grow. I would choose flowers like:

Annuals (must replant every year): buy as seed and sow in ground after all danger of last Spring frost. Some time in April for you or purchase from garden center.
Zinnia
Delphinium
Marigold
Portulaca
Geranium
Petunias
Impatiens and Begonias for shady areas

Perennials (return every season): start seed inside 12 weeks before last frost or purchase from a garden center. You can sow perennial seed directly in the ground, but they may not flower the first year.
Bee Balm
Coreopsis
Lambs ears
Chamomile
Roses (mature plant from garden center)
Phlox
Perennial Hibiscus

There really is quite a bit to choose from. Just make sure that if you choose several to go in one location that they all have the same light and moisture requirements. I started with roses because I found them easier to keep alive, but with a little experience you will be on your way to full fledged gardening.

Good Luck