Mass generation is kind of like making a big pile of toys. Imagine you have a bunch of tiny toy cars and you want to make a really big pile of them. You can't just take one car at a time and add it to the pile, that would take too long. So instead, you use a machine that can make lots of cars really quickly.
In physics, mass generation is a way of explaining why some particles, like electrons, have mass. Scientists think that particles get their mass from something called the Higgs field, which is like a giant toy car-making machine. Just like the machine makes lots of toy cars really quickly, the Higgs field makes lots of mass for particles really quickly.
But just like you need to turn on the toy car machine to make lots of cars, particles need to interact with the Higgs field to get their mass. When particles interact with the Higgs field, they get slowed down and it's like they're carrying a big backpack full of toys. That's what gives them their mass.