An oak log (via screenshot)
Oak logs are a naturally generated part of Oak trees and their wood is light brown in color. They are primarily used as building blocks and can be turned into planks by simply placing them in any crafting grid. A stripped variant can be obtained as well, but once stripped, the process can’t be reverted.
You can find oak logs in the plains biome, from oak trees. They can be picked up by breaking them with any tool but using an ax is the quickest. If you are able to get a sapling you can grow your own oak trees to farm them. Oak logs can also be found as a part of plains villages and mineshafts.
Chopping an oak tree (via screenshot)
Oak logs can be used to make Oak wood planks that can be used in any and all crafting recipes that require any form of wooden planks. They can also be used to make charcoal and as a building material. Oak logs can also be used as fuel directly without turning them into charcoal but this is quite inefficient.
Making oak planks from an oak log (via screenshot)
A. Oak logs can be found in multiple biomes and naturally generated structures, it is most common in plains biomes.
A. Oak logs can be turned into charcoal by simply smelting them in a furnace.
A. Oak trees are quite common throughout the Minecraft world making Oak logs pretty common.