Lead is a kind of metal that is very heavy. (See if you can get some lead, like a fishing weight, to see how heavy it is). People have been mining lead and using it for weights in West Asia since about 4000 BC, about the same time people started to use copper, and before they invented bronze. One early use of lead was probably for spindle whorls. Early Chinese bronze,about 2000 BC, mixed copper and lead instead of (or in addition to) tin.
Lead is pretty common all over Europe and Asia, and people used lead for all kinds of things throughout antiquity and the Middle Ages. Lead is very soft so it is easy to make things out of it. You use lead for weights on fishnets and for anchors and to weigh things, and for spindle whorls, and you use it to mend broken pottery, and for water pipes. People also used lead to clamp building stones together, inside stone walls.
Sometimes people wrote curses on little pieces of lead and dropped them into wells (so evil spirits (who lived underground) would get back at their enemies). Lead is soft and easy to work, so it was very useful.
The biggest problem with lead is that it is also poisonous. People knew this in ancient Greece and Rome, just as we know it today. They could see that when people who were enslaved were forced to go into lead mines, they got sick and died in two or three years from breathing the lead dust. Greek and Roman doctors and scientists wrote about how lead was poisonous. And that's why rich people made slaves go into the mines - free men and women wouldn't do it.
In the Middle Ages in Europe, people used to go to the old Roman buildings and dig the lead clamps out from between the stones, because that was cheaper than mining lead out of the ground. You can still see the holes in many Roman buildings, like these in the Colosseum at Rome.