To clarify the above, the tube the male has is a modification of the anal fin so it looks like a rod (a sort of primitive willy); the female has a normal triangular fin-looking fin.
Platies should not be kept in less than 10 gallons, but if you want to make room for successive generations bigger is better. 2 ft is good. If you want to breed you will also need the space for the platies to grow out and dieally two tanks so you can separate the siblings at 3-4 months old, otherwise they will start breeding with each other ad infinitum, leaving you with a lot of platies and the risk of genetic defects due to inbreeding.
Platies should be kept in a ratio of at least 2 females per male; otherwise the female will be stressed out by his constant obsession with sex. Keeping lots of females is no hardship as they are just as pretty as the males.
They can interbreed with swordtails but not with guppies.
They often eat their young so it is a good idea to invest in a small breeder trap or breeder net, not to put the female in, but to rescue the fry into after birth, away from their greedy mother.
Platies thrive on a varied diet, good quality tropical flakes, alternated with live foods and vegetables.