From the home page of your personal salesforce.com go to setup in the top right corner.
Either by searching or by finding it in the left menu under build>developed go to installed packages.
Click on the Manage Licenses link located next to ARPEDIO Matrix to add or delete user access. This is an important step which ensures proper access for the Salesforce users who need to use ARPEDIO Matrix.
In the app’s settings screen, select either Add Users or Remove Multiple users from the Licensed Users.
To add the new users, select the users and press Add.
The added users will be shown in the Licensed Users.
The Salesforce Admin can always access the Manage Licenses link in order to manage user’s access to the App by going to Setup > App Setup > Installed Packages.
Now, you're ready to add permission sets to user profiles. Here's a How-to guide.