1. Form and meaning
Partizip I is generally formed from the infinitive plus -d and often describes an action being performed: lachend. Partizip II often describes a completed action or resulting state: geschlossen. Before a noun, both forms take adjective endings according to case, gender, number and article.
When you study this pattern, identify its communicative purpose first. Then check the verb form, case and word order. German clauses are easier to control when you learn the connector together with the sentence pattern it requires.