Lava is a burning item that can be placed in a bucket. To obtain lava, you first need to craft a bucket. Get a crafting table, and then make an upside-down triangle crafted similar to a glass bottle. Click on the link of the glass bottle if you’d like to have a better view of how to craft a bucket.

Now that you got a bucket, find a pool of bright orange colored liquid. It flows slowly. Hold the bucket and right-click the lava. Now you’ve got a bucket of lava.