Question

When do you use a past participle as the verb of the sentence?

Answer 1

Question should be more understandable.

Explanation:

However, what I understand. .

Look, the bored students went into sleep during the boring lecture.
Do you noticed it "bored"? It is a past participle here. It is also derived by the verb in a sentence.

But, I guess you directly say --verb usage.
I am bored.
Here bored is used as a past participle verb by passive form.
Hope it works.