Once you have followed the download links you will be required to log into your Salesforce Organisation where you will be presented a screen similar to the one below.
Salesforce Package Installation Details screen
(note that the Professional package won’t have the unit tests or the password trigger)
Follow the Salesforce installer steps to complete package installation.
Approve Package API Access
Choose Security level
View new installed Package Details
Installed Package Detail for Enterprise / Unlimited Edition
Installed Package Detail for Professional Edition
Customize Leads Page Layout (Pre-Sitecore 9)