Yeah, I was surprised at that.
There's two game modes - Create, where you have unlimited resources and just build giant structures etc (which was what I thought the full extent of the game was), and Survival, where you have to mine or craft (ooh, I get it!) your resources, everything is finite (though the world is massive - albeit much smaller than on pc, natch) and you usually want to be inside shelter at night - when the beasties come out.
I've only played Survival.
The "story" isn't actually fed to you in any way - it's just a series of things you do that unlock new things. Effectively, you need to mine diamonds so you can get strong equipment, mine obsidian (toughest material in the game - can only be obtained with a diamond pickaxe), use the obsidian to build a portal, which takes you to a new hellish dimension, and eventually you go to a third universe where you have to fight a dragon.
Tis good - keeps it interesting and fun.
Though it's ridiculous how much fun it is even without following the story stuff, and just mining and building things. It really shouldn't work, and it doesn't sound fun at all - but somehow it works. (Or thirty million people are mistaken
)