Instructions
Obtain a lava bucket. Most lava is generated in the bottom levels of the earth, meaning you must dig down until you reach bedrock blocks, which are dark grey blocks with white and black flecks on the surface that cannot be dug. Right-click the peak of the lava while holding a bucket to fill it.
Obtain a bucket of water. This works the same as with a lava bucket, but you will need a separate bucket. You can find water commonly throughout the virtual world. If you do not want to dig for water, walk to the edge of the world until you reach the ocean.
Travel to a nearby beach or field. Any flat surface with blocks that can easily be dug, such as sand or dirt, will suffice.
Dig a 1-by-7 trench in the ground. Holding a shovel will make the process go faster, though digging the trench does not require tools.
Hold the lava bucket and right-click at one end of the trench. Wait as the lava spreads across the trench and stops moving.
Hold the water bucket and pour it over the lava. This creates seven obsidian blocks you can safely mine.