Imagine if you did something really naughty, like you ate all the cookies before dinner. Your parents might tell you that they're going to punish you for it, but then they change their mind and decide to let it go. This means they're giving you an amnesty, or forgiveness, and you won't get in trouble for eating the cookies anymore.
An amnesty law is kind of like that, but for grown-ups instead of kids. Sometimes people break the law by doing things that are illegal, like crossing the border without permission or taking part in a rebellion against the government. When lots of people do this, it can cause a big problem for the country, so sometimes the government decides to offer amnesty to forgive them and stop punishing them for what they did.
This means that the government will stop looking for the people who broke the law and won't punish them for what they did, as long as they agree to certain things. For example, they might have to register with the government or pay a fine, or promise not to do it again in the future. Amnesty can help people who made mistakes or bad decisions, but it can also be a controversial issue because some people think it's not fair to forgive someone who broke the law.