If you serve your country, an organization, or a person, you do useful work for them.

If you serve in a particular place or as a particular official, you perform official duties, especially in the armed forces, as a civil servant, or as a politician.

If something serves as a particular thing or serves a particular purpose, it performs a particular function, which is often not its intended function.

If something serves people or an area, it provides them with something that they need.

Something that serves someone's interests benefits them.

When you serve food and drink, you give people food and drink.

Serve is used to indicate how much food a recipe produces. For example, a recipe that serves six provides enough food for six people.

Someone who serves customers in a shop or a bar helps them and provides them with what they want to buy.

When the police or other officials serve someone with a legal order or serve an order on them, they give or send the legal order to them.

If you serve something such as a prison sentence or an apprenticeship, you spend a period of time doing it.

When you serve in games such as tennis and badminton, you throw up the ball or shuttlecock and hit it to start play.

When you describe someone's serve, you are indicating how well or how fast they serve a ball or shuttlecock.

If you say it serves someone right when something unpleasant happens to them, you mean that it is their own fault and you have no sympathy for them.