(someone) could have (done something)

You say that you "could have" done something when you realize that there was a better day to do something, after you did it. For example, if a good friend is visiting your city and you find out that they got a hotel room, you can say:

You could have stayed with us.

order (food)

You use the word "order" for when you ask for food at a restaurant:

What are you going to order?

You can also order things to be delivered to you, like food:

Why don't we order a pizza?

Things that get delivered in the mail can also be "ordered".

split (something)

To "split" something means to share it equally between people. It's often used in a restaurant setting. Things that people often "split" include:

• split an appetizer (at a restaurant)
• split a dessert
• split the check

You can split something with another person:

Do you want to split this with me?

Or you can split something between a group of people:

We'll just order a few salads and split them between us.