When you click on the button, you will have a choice between installing authentication via mail or via an application on your phone.
When choosing authentication via mail. A letter with a code will be sent to your mail specified during registration, which will need to be entered in the field on the site.
When you select phone authentication. Download the Authy app or Google Authenticator to your phone. Scan the QR code from the site in the application, then enter the received code from the application into the form on the site.
Save the backup codes in a safe place, they will help you log into your account if you lose mail or if you lose the application on your phone.
Download the game client in any way you like. This usually takes 20-30 minutes.