He blamed me for the accident, is in the active voice. ('He' is the subject of the verb and is performing the action; 'me' is receiving the action of the verb.)
I was blamed for the accident, is in the passive voice. (In this case the subject of the verb ('I'), does nothing. The subject is being acted upon.
Please note that in the active voice we learn who is doing the blaming and who is receiving the blame. In the passive voice we only know who is receiving the blame.