Advice on taking care of dogs?

i have this dog hes an adult german-sheperd my uncle droped him of before he went to prison, but apperantly me and the dog dont get along. He has been getting really agressive so i took him to my backyard and i keep him there all the time. i remember my uncle told me about him going hunting with je'mal, the german sheperd and he told me that he killed a cayote and he told me to be careful, but i dont know what that means.Two weeks ago i went to go feed him, as i opened the door je'mal ran inside the house and killed my cat and today he was growling at me wail i was giving him water, he was showing me his teeth so i ran inside the house but je'mal got in as well. i ran into my computer room. i came out with an umbrella from the computer room to see if hes calmed down, i noticed that all the cords were ripped out including the phone cords. i saw him in my room he jumped of my bed so i threw my umbrella at him and ran inside my computer room. iv been stuck in my computer room for over three hours and im scared shitless i dont know what to do next. someone please help me!!!!!!