Rebirth in Buddhism means that after a person dies, their energy or life force doesn't end, but instead moves on to another life. It's like when a caterpillar becomes a butterfly, but instead of just changing form, a person's energy moves into a new body and continues on.
Buddhists believe that our actions in one life, known as karma, affects our future lives. So if someone is kind and does good things in their current life, their future lives will be happier. But if someone is mean and does bad things, their future lives will be harder.
The goal of Buddhism is to break the cycle of rebirth, which is called samsara. Buddhists believe that by following the Eightfold Path and achieving enlightenment, they can escape samsara and reach a state of nirvana, where they are at peace and free from suffering.
But even if someone doesn't achieve enlightenment in their current life, they believe that their actions will still affect their future lives, so it's important to be kind and do good things now.