Online activation is the easiest and fastest way to get up and running with Unity. Below is a step-by-step guide on how to activate Unity online.
Download and install the Unity Editor. The latest version of Unity can be found here.
Fire up the Editor from your Applications folder on OS X or the shortcut in the Start Menu on Windows.
Firstly, you will encounter the ‘Unity Account’ window. Here you will need to enter your Unity Developer Network, Google or Facebook account credentials. (If you don’t have an existing Unity account or have forgotten your password, simply click the respective ‘create one’ and ‘Forgot your password?’ links. Follow the onscreen prompts to create or retrieve your account.) Once your credentials are entered, you can proceed by clicking ‘Sign in’.
You will be faced with a window titled ‘License management’. Select the version of Unity you wish to activate and click ‘Next’.
You will now be able to proceed to the Unity Editor by clicking the ‘Start using Unity’ button.
For any further assistance, contact support@unity3d.com.