Okay kiddo, so first of all, Dartmoor is a big area in England with lots of hills and fields. A long time ago, people discovered that there was something very valuable in the ground there called tin.
Tin is a metal that can be used for making lots of things like pots and pans and other stuff. So people started digging into the ground to get at the tin. This was called tin-mining.
The people who did the mining were called miners, and their job was to dig tunnels and shafts into the ground to find the tin. They had to use special tools like picks and shovels to dig through the dirt and rocks.
Sometimes, the miners would find big veins of tin that ran deep into the ground. They would have to dig really deep tunnels to get to the tin. Imagine digging a really deep hole in the dirt with a big shovel - it would take a lot of work!
Once the miners had found the tin, they would dig it up and bring it to the surface. Then, they would wash the tin in water to get rid of any dirt or rocks that were still stuck to it. After that, the tin was ready to be shipped off to factories where it could be turned into useful things.
Tin-mining was a really important industry in Dartmoor for a long time. People relied on it to make a living and provide for their families. Even though tin-mining isn't done as much anymore, it's still an important part of the history and culture of Dartmoor.