In general we can say that perfect participles are formed with
the prefix ge- + past tense stem of verb + suffix

Most weak verbs (again we have the distinction!!!!) have the suffix -t.

warten => gewartet kaufen => gekauft hoffen => gehofft putzen =>geputzt sagen => gesagt lachen => gelacht planen => geplant weinen => geweint malen => gemalt bauen => gebaut to wait => waited to buy => bought to hope => hoped to clean => cleaned to say => said to laugh => laughed to plan => planned to cry => cried to paint => painted to build => built