Legal separation is when two grownups who are married decide they want to live apart from each other, but they don't want to get a divorce. It's just like when best friends say they want some space to think about things on their own but still want to be friends.
When two married people legally separate, they make a bunch of important decisions together, like who will get to live in the family home, how much money each person will get from the bank account every month, and who will take care of the children.
They also create a legal agreement called a Separation Agreement that lays out all the rules they will follow while they are living apart, like who will pay for child support, health insurance, and other expenses.
The reason why some married people choose legal separation instead of divorce is because they still believe there's hope for their marriage and they want to give it a chance. It also gives them a chance to live separately for a while to see if they can make things work, without worrying about being officially divorced, which can be very hard to undo.
However, even if they're legally separated, they are still married in the eyes of the law, which means they can't get married to other people unless they officially divorce first.