Hey, umm, that game you're talking about is world 3. World 2 is where you join a guard team (either Gold Hawks, Blue Falcons or Black Swords) and you get their mascot digimon (GH=Agumon, BF=Patamon,BS=Demidevimon) and then you have to complete domains, which are like caves and dungeons pretty much, And you get this Tank-Like vehichle called a Digi-Beetle. It has a battery, cannons, engines and moer which are all upgradable and customizable. You travel through the Domains with this.
When you go through the domains, you will enconter many digimon, each catchable. You get itto join your team by giving it gifts before you beat it in battle. The only digimons you cant catch are the bosses.
Also, this game lets you experiment with DNA Digivolving! Regular too.
Overall, pretty good game. The graphics are kinda bad, but what do you expect from a PS1 game?