'We' is the first-person plural pronoun in the nominative or, as it is often called in English, the subjective, case.
In other words, 'we' is the word used to represent 'you and I' as the subject of a sentence. The 'you' in this instance may be one or many.
We are going to the store.
We love to fly kites on windy March days.
To represent the same people as the object of a verb or a preposition, the word 'us' is used.
Please tell us what you would like from the store.
Come with us to the park to fly a kite!