The past participle is formed by adding '-ed' to the end of regular verbs: asked, walked, wanted. You have to learn the past participle of irregular verbs separately. If you have a list of irregular verbs, the past participle is the third column.
Now the use:
We use the past participle to form perfect tenses: have + participle.
I have never BEEN to Paris. The train had LEFT when I arrived.
Also in passive sentences: to be + participle.
Hamlet was WRITTEN by Shakespeare. My car has been STOLEN.
I found this, maybe it will help-
Past Participles usually are formed by adding ed to the verb base. The past participle of hunt is hunted. Past participles function in three ways.
example: Hunted by lions, the antelope scattered into the trees. The past participle hunted is part of a phrase that modifies antelope. It's an adjective.
example: The hunted antelope scattered into the trees. Here the past participle is a one-word adjective.
example: The lions have hunted antelope. The past participle hunted is part of the main verb (have hunted).
example: The antelope will be hunted. The past participle hunted can be considered part of a passive verb or an adjective (better to consider it part of the transitive passive verb will be hunted so that you recognize the transitive active verb).
example: The antelope that was hunted today was male. The dependent clause that was hunted today can be simplified to the past participle phrase hunted today: The antelope hunted today was male.