First you must download the Respondus program to your computer. 

Once the installation finishes, you need a password and the Product ID# to activate the installation. The Product ID# is presented to you the first time you open the Respondus program. You will receive the password once you have purchased a permanent activation password or a 30-day trial password.

You can obtain a password by following this link: http://respondus.com/download/respondus.shtml. 

Follow either link shown on the screenshot below to register. You must provide an email address and the Product ID# that displays on the opening screen of Respondus. Once the information is submitted, the activation password is sent to the email address you specified.

Once the password is received, enter it into Respondus. Start Respondus and enter the password when prompted. You may want to copy and paste the password from the email message to prevent typing mistakes. Click "OK" to continue. The Respondus software is now activated.