How is the perfect tense formed in German?

To form the perfect tense in German you use an auxiliary verb, either 'haben' or 'sein', plus the past participle of the main verb in the sentence. Most verbs take 'haben' when used in the perfect tense, but the auxiliary verb 'sein' is used with verbs which indicate movement or a change of state, such as the verbs 'gehen' ('to go', indicates movement) and 'aufwachen' ('to wake up', indicates a change of state). In terms of word order, the past participle normally comes at the end of the sentence (Ich bin ins Kino gegangen), however when the perfect tense is used in a subordinate clause the auxiliary verb comes at the end (weil ich ins Kino gegangen bin). Most past participles of verbs in German are formed by placing 'ge' in front of the infinitive, and either leaving the ending of the verb as 'en' (lesen - gelesen) or replacing the 'en' with 't' (spielen - gespielt). However, there are a huge number of exceptions, including past participles which change letters in the stressed syllable of the verb (denken - gedacht), or even verbs whose past participle is the same as its infinitive (vergessen - vergessen).