The present participle is always used as an adjective and describes what the noun is doing right now.
The past particle is normally used to construct the perfect, past perfect, or passive, but it can also be used an adjective. When being used as an adjective, the past participle expresses what the noun has already done or had done to it..
Present Participle: „Das weinende Kind ist in der Küche.“ (the kid is crying right now)
Past Participle: „Das gestohlene Auto ist hier.“ (the car was stolen)
The present participle tells you what the noun is doing at the moment (while the other action - the conjugated verb - is also going on). This is just like the "-ing" form of the verb in English.
When it comes before a noun, it has to be declined (just like every other adjective).
The past participle, when used as an adjective, signals that the noun has a certain status/condition or describes an action that already occurred. This is done in English with the "-ed" ending.
= Before she became a professor, she was educated.
= Before I bought the house, it was renovated.
Present Perfect as Adjective: Things happen simultaneously.
Past Perfect as Adjective: Things don't happen simultaneously.
A detailed explanation of the rules for adjective declension.
An overview of what you have to pay attention to when dealing with adjectives in general.
Adjective declension depends on whether there is a definite article, indefinite article (including possessive determiners or the negative article), or no article at all (the zero article) in front of the adjective.