There are three ways to form the past participle in German:
1) For "weak" (regular) verbs add ge- as a prefix and -t as the suffix. Examples: lieben (to love) --> geliebt , kochen (to cook)--> gekocht.
2) For strong verbs, add ge- as a prefix and -en as the suffix. Examples: fahren (to drive) --> gefahren , trinken (to drink) --> getrunken.
3) Irregular verbs will maintain the ge-prefix but the stem of the verb may be altered. In addition, a ge- prefix is not necessary when the first syllable of the verb is unstressed. For example, verschlafen (to oversleep) does not need the ge- prefix because it's first syllable "ver" is unstressed.
