The Install CRM Solution button will allow you to manage the roles of a websites' users. Without a CRM Solution, you would be unable to manage user roles.
In order to install a CRM Solution, you must first navigate to the Portal Connector Configuration settings under the Settings & Configuration option which is under the Administration tab.
Once there, make sure you're on the General Settings page which is under The Portal Connector collapsible tab. Then, click on the Install CRM Solution button to install your CRM Solution.