i'll explain a little bit about each season so u can keep track. 2 avoid major confusion, i'll use each season's Japanese tile
DIGIMON ADVENTURE
7 kids at summercamp (Tai, Sora, Matt, Izzy, Mimi, Joe, and Matt's little brother T.K. [and eventually Tai's little sister Kari]) r unexpectedly wisked away 2 the Digital World, where each of them receives a Digimon partner. Throughout their journey 2 find a way home (and even AFTER they get back home), they have 2 do battle against many major Digimon villains such as Devimon, Etemon, Myotismon, and others.
DIGIMON 02
It's 3 years later, and the characters r older (T.K. and Kari especially look visably older), and an evil human kid called the Digimon Emperor (who turns out 2 b boy genius Ken, who later turns good and joins the good guys) is trying 2 take over the Digital World. T.K. and Kari team up w/ 3 new kids (Davis, Yolie, and Cody, who each recieve their own Digimon partner), and are able 2 transport 2 and from the Digital World in order 2 fight Ken, and later on Arukenimon, Mummymon, and a mysterious, pale human Oikawa
DIGIMON TAMERS
Probably the most complex season of all. Tamers takes place in the "real world", where Digimon is merchandised and is a popular tv show and card game. When Takato draws up a Digimon of his own creation, it magically becomes a REAL Digimon 2 call his own. He quickly meets 2 other kids (Henry and Rika) w/ their own Digimon, as well as 2 tamerless Digimon (the cute, cuddly Calumon, who seems 2 b able 2 help Digimon digivolve (power up and become stronger) and the dark, snot-nosed Impmon). On the Digimons' tail is a secret organization called HYPNOSE, led by the mysterious Yamaki. When the powerful Digimon Devas invade the real world, many battles ensue, and Yamaki and HYPNOSE turn out 2 b good guys, and r actually the CREATORS of digimon, and when Calumon is kidnapped, Takato, Henry, Rika, and Takato's friends Jeri, Kenta, and Kazu (and eventually Henry's baby sister Suzie) must journey 2 the Digital World 2 save him. This series is centered mainly on the card game, as the kids can slide cards from the game through a device in order 2 power up their digimon in battle.
DIGIMON FRONTIER
(bear w/ me that i've only gotten to c 5 eps so far) Yet another alternate universe season. 5 kids (Takuya, J.P. Zoe, Tommy, and lone wolf Koji) somehow find there way on2 a train that takes them 2 the Digital World, where they meet the arguesome Bokomon, keeper of the book, and Neemon, keeper of his pants. In this series, the kids obtain 5 spirits of the 10 Legendary Warriors, and r able 2 use these spirits 2 actually BECOME Digimon warriors at will, in order 2 do battle against such evil Legendary Warriors such as Grumblemon, Ranamon, and Mercuremon.