The blocky world of Minecraft offers many activities you can engage in. You can start a building project to make a castle, town, or even a city, or you can take the peaceful route and start a farm.
You are going to need a lot of blocks for this build so you should better get to farming. As for the blocks themselves, you can pretty much use anything. Cobblestone and Wood are the most common ...
To make a mob farm in Minecraft that automatically spawns and kills enemies, you'll need stone, trapdoors, chests, hoppers, slabs, and water.