What do we mean by the phrase "être verbs" when using the perfect tense in French?

When using the perfect tense in French, there are three components to a phrase. The first is the pronoun (I, you, he/she, we, they). The second is the auxiliary verb, and the third is the past participle. When one refers to an être verb, it means that the phrase in the past tense takes être as its auxiliary verb. This is less common in French than the use of avoir, the alternative auxiliary verb in the perfect tense. In order to use être as the second part of the past tense phrase, it must be conjugated into the present tense (je suis, tu es, il/elle/on est, nous sommes, vous êtes, ils/elles sont) and used after the pronoun. For example, the verb "to go" translates to "aller" in French, and this is an example of an être verb. So "I went" would translate as "je suis allé" in French. It is also important to remember that unlike verbs which take avoir as an auxiliary verb, verbs that take être must agree with the pronoun they are describing, with the addition of an e (for feminine singular pronouns), an s (for masculine plural pronouns), an es (for feminine plural pronouns), or nothing at all (for masculine singular pronouns). For example, the translation of "she went" is "elle est allée".