Platies and Corydoras are smaller tropical fish quite commonly bought by new fish keepers.
They like a minimum of a 10gal aquarium with a heater and filter, preferably larger and of course this also depends how many you have. 3 platies and 5 corydoras would be ok in 10gal (uk)
They feed on most normal fish food - flakes, sinking pellets and other small foods like frozen daphnia or bloodworm.
They need a temperature around 24 deg.C
You need a good tank regime - water change 25% and gravel vac at least once a week using a decent dechlorinator.
They prefer sand or smooth gravel substrate and like places to hide like caves and plants.
Platies are livebearers which means they give birth to baby fish (fry) and will do so at least once every 4-6 weeks if you have both male and female.
Corydoras lay eggs and don't breed quite as easily but many people do breed them fairly easily.