Gremple is a conjugator that provides Partizip II (the so-called past participle) and the four simple tenses of a verb namely Präsens (present), Präteritum (past), Konjunktiv I and Konjunktiv II. The compound tenses are not provided because they are always regular and the same for all verbs.
If you enter a verb with the "show how" button, gremple will demonstrate how to derive the conjugations from the minimal information it stores for the verb. This minimal information allows you to see easily the irregularities of each verb and learn how to conjugate it yourself. For full details see here.