To put emphasis on who or what is doing the action:
I watched Harry Potter and the Chamber of Secrets last night. (Active voice)
To put emphasis on who or what the action was done to:
Harry Potter and the Chamber of Secrets was watched by me last night. (Passive voice)
To put emphasis on when or where the action occurred:
Last night, I watched Harry Potter and the Chamber of Secrets. (Active voice)
OR
Last night, Harry Potter and the Chamber of Secrets was watched by me. (Passive voice)
I’m not really sure what you were trying to ask, but I hope that helped!