Time Managing school and extra-circulars?

So i need help, I am in grade 11 going to grade 12, and i need help on time management. i am always on the computer and i need to stop. I get so lazy when i get home. I have a piano exam coming up and i didn't memorize anything. and i have school work, that i need to do. I don't how to manage it. how do i start. what to do. i need someone to help me make a timetable. i get home around 3-4 pm and then i don't know what to do, cause they tv and internet distracts me so much. help. thanks.