The word order has several meanings:

1. A command or instruction. When a teacher gives an order to line up for recess, students are expected to follow that direction. A general might order troops to move to a new position. Parents order their kids to clean their rooms (though kids don't always listen!). An order carries authority: it's not a suggestion or a request, but an instruction that should be obeyed.
2. Arrangement or organization. When your desk is in order, everything has its place and you can find what you need. Things happen in order when they follow the right sequence: first you crack the eggs, then you beat them, then you cook them. Scientists classify living things using a system where an order is a group of related families (like how cats, lions, and tigers all belong to the order Carnivora). Teachers might ask you to put your spelling words in alphabetical order.
3. A request to purchase something. When your family orders pizza for dinner, you're asking the restaurant to prepare food for you. You might place an order for new books online. A restaurant takes your order when they write down what you want to eat.

The phrase law and order means a society where rules are followed and enforced. When something is out of order, it's either broken (like a vending machine) or not working properly, or happening in the wrong sequence (like telling the ending of a story before the beginning).