1. Past participles may also be used as adjectives, just as they can in English. You will usually not find these adjectives listed separately in your dictionary; you are responsible for recognizing them as participles functioning as adjectives, and for using the dictionary entry for the infinitive form of the verb to look up their meaning.
Das Fenster ist geschlossen.
The window is closed.
ein gekochtes Ei
a boiled egg
The first example should not be confused with the present perfect tense. Keep in mind that the verb schließen uses haben as a helping verb, not sein, to form present perfect tense. Since it is grammatically (and sensibly) impossible to read this as a verb, it is apparently being used as an adjective; it tells you the condition of the window, not what is happening to it.
2. Past participles may also be used as adjectival nouns.
As you learned in Unit 4, you can recognize adjectival nouns from their normal noun capitalization and syntax position, but with the addition of an appropriate adjective ending. Thus, for example, in nominative case:
das Geschriebene (from schreiben – to write)
[literally:] the written / [usually:] that which was written / [or:] what was written
das Gesagte (from sagen – to say)
[literally:] the said / [usually:] that which was said / [or:] what was said
In the next example, you should recognize nouns formed from the verbs fangen and sagen:
Der Gefangene entnahm dem Gesagten, daß es spät war.
The prisoner gathered from what was said that it was late.