Instructions
Craft a pickaxe. The material of the pickaxe does not matter, because you are not harvesting anything; even wooden pickaxes will mine stone.
Right-click any crafting table. Place one iron ingot in the center square of the bottom row of the crafting grid that appears. Place one iron ingot in the first and third squares of the center row. This crafts a bucket, necessary to transport lava.
Hold the left mouse button on any block to dig. You must dig all the way down to bedrock to easily find lava. Bedrock are black, grey and white blocks that you cannot break. These are found scattered abundantly in the bottom seven layers of the level.
Dig around the bottom seven layers until you come across lava. One major telltale sign is finding obsidian and diamond ore. Obsidian blocks are deep purple blocks and diamond is grey with light blue flecks.
Hold the bucket in your hands and right-click the lava to fill the bucket. Right-click any area while holding the bucket to deposit the lava in that spot.