You gather resources to build structures and tools to make it easier to gather resources.
The whole world is made of cubes, so you can pick up a cube of dirt and put it somewhere else. Repeat and you can flatten a hill. Or you can mine stone to build a house or fortress.
There are animals in the world, some are hostile some aren't. You can farm the peaceful ones for food. The overall "goal" is to build powerful weapons and cross dimensions to slay a dragon, but for many people just building themselves a cool house or town is enough.
I play on a "creative" server with no monsters, and it's like having unlimited Lego bricks to building anything you like! My friends and I have built a huge city.
It is a lot more fun to go and try it for yourself.