You use at to indicate the place or event where something happens or is situated.

If someone is at school or college, or at a particular school or college, they go there regularly to study.

If you are at something such as a table, a door, or someone's side, you are next to it or them.

When you are describing where someone or something is, you can say that they are at a certain distance. You can also say that one thing is at an angle in relation to another thing.

If something happens at a particular time, that is the time when it happens or begins to happen.

If you do something at a particular age, you do it when you are that age.

You use at to express a rate, frequency, level, or price.

You use at before a number or amount to indicate a measurement.

If you look at someone or something, you look towards them. If you direct an object or a comment at someone, you direct it towards them.

You can use at after verbs such as 'smile' or 'wave' and before nouns referring to people to indicate that you have put on an expression or made a gesture which someone is meant to see or understand.

If you point or gesture at something, you move your arm or head in its direction so that it will be noticed by someone you are with.

If you are working at something, you are dealing with it. If you are aiming at something, you are trying to achieve it.

If something is done at someone's invitation or request, it is done as a result of it.

You use at to say that someone or something is in a particular state or condition.

You use at before a possessive pronoun and a superlative adjective to say that someone or something has more of a particular quality than at any other time.

You use at to say how something is being done.

You use at to show that someone is doing something repeatedly.

You use at to indicate an activity or task when saying how well someone does it.

You use at to indicate what someone is reacting to.