In Blender — the open-source, 3D creation software — you rotate the viewport by pressing down on your mouse’s scroll wheel. Problem is, on Apple products, such as the trackpad or Magic Mouse, there is no such thing as a scroll wheel.
To rotate your viewport in Blender on a Mac, you can turn on an option that will let you emulate a “3 button mouse”. To turn this option on, you’ll want to go to File > User Preferences…, then when the preferences window shows up, click on the Input tab and make sure to check the Emulate 3 Button Mouse under the heading Mouse.
Now in your viewport, you can hold the option key and the left mouse button on the Magic Mouse or click on the trackpad on a MacBook to rotate it.