Instructions
Double-click the "Minecraft" desktop icon. Wait for the program to load.
Type in your login information. Click "Login." Wait for the server to connect and the menu to load.
Click "Single Player," followed by the world in which you want to play. Wait for the world to load.
Press the "Esc" key and click "Options."
Click "Difficulty" until it reads "Difficulty: Peaceful."
Click "Done" when you are finished.