Participles as adjectives: spannend, gespielt

The Partizip I is the infinitive + -d: überzeugen → überzeugend (convincing), spielen → spielend (playing). It describes something that is happening at the same time, or has an effect, like English “-ing”: spielende Kinder (children playing), ein überraschendes Ende (a surprising ending).

The Partizip II is the past participle you know from the Perfekt. As an adjective it usually has a passive meaning, something that has been done: die versteckten Briefe (the hidden letters), ein gut gemachter Film (a well-made film).

Before a noun, both participles take the normal adjective endings: ein spannender Film, die passende Musik, mit dem reparierten Fahrrad. After sein, werden or finden they have no ending: Der Film ist spannend.

In newspapers, reviews and official texts, a participle before a noun often has more words in front of it: der in nur sechs Wochen gedrehte Film (the film shot in only six weeks). English puts this information after the noun.

To understand such a phrase, find the article, jump to the noun, and read the words in between as a relative clause: der Film, der in nur sechs Wochen gedreht wurde. In speech people use relative clauses; you mainly need to recognise the long phrases.