The past participle doesn’t need any extra letters as the subject is a singular male. Nous sommes sortis. An -s is needed on the end of the past participle if it is all masculine or a mixed group of ...
The perfect tense is used to say what you did or what you have done in the past. To form the perfect tense you need a subject, an auxiliary verb and a past participle. Perfect tense with 'être' in ...