There are LOTS of guppy forums out there, Abby. :) BUT - I have guppies, so I will try to help you out a tad. 10 gal. is good, 20 gal. is better, I feed New Life Spectrum Growth Formula in the morning & Ocean Nutrition Formula Two flakes in the evening. Tank temp 78 - 80 is good.
If you get two or three of the same sex, a 10 gal. is GREAT. If you get a male & 2 females (the preferred ratio so the males don't harass the girl/s to death), be prepared to have TONS of babies - no special care required except maybe putting a foam over the intake on the filter so the babies don't get sucked up.
PLANTS - they LOVE plants and floating plants are GREAT for helping hide babies from hungry parents. Guppy grass is really good for this!
Good luck & have fun with them!