Participles before a noun
Partizip I describes an ongoing active action and is formed from infinitive plus -d. Partizip II often describes a completed or passive action. Used before a noun, both need adjective endings.
Understand the idea
Participles can describe a noun more compactly than a relative clause. Partizip I commonly presents an ongoing active action, while Partizip II often describes a passive or completed relationship. The exact interpretation also depends on the verb.
Build it step by step
Form Partizip I from an infinitive plus -d, then add the required adjective ending. A Partizip II used before a noun also takes adjective endings. Determine gender, number, case and article pattern just as for any attributive adjective. Longer participial phrases place their additional material before the noun.
See it in a sentence
Die wartenden Gäste stehen vor der Tür.
Das schlafende Kind sitzt im Zug.
A useful memory aid
Expand the phrase into a relative clause first. Check whether the noun performs the action or is affected by it, then compress the description again.
A common trap
Do not omit the adjective ending from a participle before a noun. Also do not assume every Partizip II is passive; intransitive verbs can express a completed change or state.