How do you conjugate the passé composé in French and what is it used for?

The passé composé (sometimes called the perfect tense) is used to describe an action in the past which has finished. In order to form this tense there are three parts of the verb-the subject, the auxilary and the past participle. for the majority of verbs, avoir is used as the auxiliary verb however there are some verbs which require the present tense of être (we will come to these verbs later). If you wanted to say 'he watched tv' you would need the 'he' form of the verb,the auxiliary and the past participle. In this case the he form is 'il', the auxiliary is 'a'. This is literally translated as 'has'. The past participle is 'regardé'. The literal translation is 'he has watched (TV)'. To form the past participle of regarder, you remove the infinitive ending (er) and add on the past participle ending which is é. I hope this helps, there are also many irregular verbs which require different endings but this is a good start to try and understand the concept of the perfect tense.