When we want to use a paper or document in another country, we need to make sure that it's real and important. To do this, we legalize the document. It's like putting a special sticker on it that says "this is real and you can trust it."
First, we ask the government to check if the document is real and important. Then they put a special stamp or signature on it to show that it's been checked. This makes the document official and legal.
Now, when we show the document to other people in another country, they know that it's trustworthy and real. So, when we want to travel, work, or study in another country, we need to legalize important documents like our birth certificate, diploma, or marriage certificate so that we can use them there.