How is the perfect tense constructed?

The perfect tense is made up of two parts: the auxiliary (helping) verb and the past participle. These are two separate words and must both be present to construct the perfect tense. The auxiliary verb is either avoir or etre, but usually it is avoir. This must be conjugated in the present tense according to the the subject in the sentence. The past participle ends with either é, i or u depending on whether the verb is er, ir or re. For example: I bought a hat - J'ai acheté un chapeau. Ai is avoir, the auxiliary verb, and acheté is the past participle, and ends with é because acheter ends with er.