The third form (the past participle) is used in all perfect tenses:
The same form is used in the passive voice:
Both these sentences are in the present progressive tense. The girl's sentence is in the passive voice. She isn't doing anything - she is the receiver of the action.
The third form stays the same in all tenses:
We don't use the passive voice with the future progressive (be being) or the perfect progressive tenses (been being). In such situations we need to make a different sentence to communicate our idea.
We can add information about the person or thing doing the action:
It's the same preposition we use to name the author of a book, piece of music, painting etc.:
The same 3rd form can also be used as an adjective:
It can be confusing, so don't worry if they look very similar.