How to find lava pool?

Run around in a desert, plains, or savana (they are most likely) you can also dig down to find one

Thanks

If you're searching for surface exposed lava pools, make sure to search in either a plains or savanna biome, and preferably a desert biome (like Acnnx pointed out), as lava pools spawn slightly more frequently in plains and savanna biomes, while they spawn twice as frequently in desert biomes compared to other biomes. So if you're searching for a surface exposed lava pool, a desert is definitely the right place to search.

And as Acnnx also points out, you can also dig down to find lava pools or lava caves. Lava is also far more common at lower Y-levels, but tend to take as much if not more time to locate because you have to dig a lot. But, you shouldn't just dig down at a random spot, because lava caves & pools tend to spawn below the starting point of caves. I've linked a video below by k4yfour where he explains in further detail how to identify the starting point of a cave:

Another good tip to keep in mind is mining at Y-level 11 only, (you can see the Y-level by pressing F3, in the top-left corner where it says XYZ:, or Block:), because this is the level above where lava appears in caves, and this ensures that you don't mine directly into lava. And yet another good tip is to play with subtitles on, (it can be enabled in the "Music & Sound", or "Accessibility Settings" section of the Options menu). Often times you'd miss lava pools or lava caves because you simply can't hear them, but using subtitles it'll show you in the bottom-right corner what sounds are audible at a given time. Keep an eye out for the "Lava pops" message which indicates that lava is nearby.