Back during the mid-late 1990s, V-Pets (also called 'Giga Pets', 'Virtual Pets', 'Electronic Pets' etc) were everywhere, it seemed. On such V-Pet was called Tamagotchi, made by Bandai. In it, you raised a cute little creature that grew up in different ways depending on how you cared for it. Well, one day, they decided to take the Tomagotchi a step further (possibly to market more to guys; girls seemed to be the main consumers of the original giga pets). They called it "Digimon: The Original Battling Digital Monster". The basis was almost exactly the same as the Tomagotchis, only not all of the creatures were so cute & cuddly, plus there was a port on the top of the device, allowing two to be connceted together and battle it out.
Digital Monster 1
The first, and byfar the most common of the digimon v-pets. It consists of a small device with an LCD screen on the left side and three buttons on the right. The original v-pets came in a huge variety of colors, so it would be difficult to list them all. You can tell version 1 easily, however, because it has Koromon and Tyrannomon on the box. I think you can still find them on eBay, though they seem to be dwindling more and more. Consider yourself especially lucky if you can find one of the other versions. Anyways, when you first start your little pet up, and egg appears on the screen, and a little Botamon will hatch. From there, how you care for it determines what creatures it evolves to.
Digital Monster 2
This version is considerably more rare than the first. I happen to have found one, and I'm lucky to have done so. Anyway, it's very similar to the first version. The only differences are the creatures available, and the training system is a bit different. I've seen this version in one of three color schemes: white with black trim, black with white trim, or clear with black trim. It has Tsunomon and Garurumon on the box.
Digital Monster 3
Again, very rare. I don't have any of the other versions besides 1 and 2, so I don't know a lot of differences it has with earlier versions. I do know its either orange with purple trim or vice versa. Tokomon and Ogremon are on the box. Note that since the anime hadn't come out yet, don't expect all of the digimon to follow the same evolutionary lines; for example Patamon is in this version, but no Angemon.
Digital Monster 4
I know next to nothing about this version, save for the digimon in it.
Digital Monster 5
The rarest of the rare. I know only a very limited number of these were made, and I've never seen them for sale anywhere.
As I mentioned before, the big difference in each version is the digimon that are in it. All of the digimon in each version correspond to each other and are virtually equivelent to those in other versions. Here's a chart that should clear that up and show which digimon are equivelent to each other:
Now I'll tell you how to aquire each digimon. Refer to the chart to see which digimon I'm talking about for each version. For example, if I say 'Adult B', then I'm referring to Devimon on Ver.1, Angemon on Ver.2, etc.
Baby 1: Hatches from the egg. You don't have to do anything special.
Baby 2: Evolves from the baby in about one hour. I don't even know if its possible for the Baby to die beforehand. unless you completely neglect it, it should always evolve to its Baby 2 stage.
*Child digimon take about 1-2 days to evolve from Babies.*
Child A: Take good care of your Baby digimon.
Child B: Take poor care of your Baby digimon.
*Adults take another 3 days to mature.*
Adult A: One of the easiest for me to get. Take good care of Child A. Feed him whenever he's hungry and train him a lot. Also be sure to clean up after him and turn the lights off when he goes to bed.
Adult B: Take good care of Child B in the same manner described above for Adult A. It may also evolve from Child A if you don't train it enough.
Adult C: I have no idea here. I've never been able to get one. All I know is it'll only evolve from Child B.
Adult D: I'm not absolutely positive on this one, but I know you have to take mediocre care of Adult A. Don't train much, if at all (use vitamins to keep its strength up instead of training it.).
Adult E: Very similar to Adult D, only it seems to occur more often than Adult D & F, and it can evolve from Child A or B.
Adult F: Again, so-so care of Child B.
Adult G: Take really bad care of Child A or B. Don't feed it often, let its crap pile up before cleaning it, and wake it up when it tries to go to sleep.
*Perfects take about 3-5 days to evolve, if they do so at all... :(*
Perfect A: Evolves from Adult A, B, or C. You have to take excellent care of it, and make it fight a large number of battles.
Perfect B: Evolves from Adult D, E, or F. You have to take excellent care of it, and make it fight a large number of battles.
Perfect C: Evolves from Adult G. You have to take excellent care of it, and make it fight a large number of battles. This is easier said than done because Adult G is typically much weaker than the others.