Okay kiddo, so imagine you had a friend who was really mean to you and you wanted to make sure they got punished somehow.
Well, a long time ago, in a place called Pella (which is now in modern-day Greece), people had a similar idea. If someone felt like they had been wronged, they would write their complaint on a piece of lead (kind of like a heavy metal), and then toss it into a sacred well or spring. This was meant to curse the person who had done them wrong.
These pieces of lead with curses written on them are called "Pella Curse Tablets".
The tablets usually had something like, "May so-and-so never find love again!" or "May so-and-so never have a child!" written on them. People believed that once they threw the tablet into the water, the curse would come true and the person who wronged them would suffer the consequences.
It's important to note that the people making these tablets believed in various gods and goddesses who they thought had the power to make these curses come true. So it was a way for them to ask the gods for help in getting their revenge.
Nowadays, we don't really use these types of curses anymore (and it's not very nice to wish bad things on other people), but historians study these Pella Curse Tablets to learn about what life was like a long time ago and what people believed in.