English has many flaws. One is that the set of pronouns is incomplete. They cannot be used for every situation. Pronouns are those words used to replace a name, or names, to make speaking faster and easier; for example: I, you, him, they...
The pronoun we is used to refer to a group of people that includes the person speaking. However it does not clearly show if it includes the person being spoken to or not.
For example: We are going to have a maths test next week.
It could mean my classmates and I will have the test, but not you. The person being spoken to might be the child's mother. It could also mean the person being spoken to is a classmate and is being told about the test.
The same problem occurs with the word us, which is a form of we. The word we is used for the subject of the sentence and us is used for the (direct or indirect) object of the sentence. Both we and us are from Old English and using different words (with a different case) for the same thing in the subject and the object of a sentence is a feature of Old English. Modern English has simpler grammar, but the old forms are kept for many pronouns. The same problem occurs with the other plural pronouns. The word ours can mean: my group's and not yours, or yours and mine.
Usually we or us refers to a group of people. There is an exception. A queen or king can use we or us to refer to themselves because they are the symbol of the whole population of the country. Elected officials do not use this form. However Queen Elizabeth may use we to refer to herself, but ordinary people such as you and I cannot. This usage is called the royal we and has been used in English for more than a thousand years. Sometimes people whose name is not Elizabeth use the royal we, but it sounds very pompous. A person who is pompous thinks that they are very important.
When using the words we and us, keep in mind that context should tell the listener if they are being included or not. In the sentence: We are going to see a movie. Are you telling the person to come with you or not bringing them?