Plauti Deduplicate Permission Set
The easiest way to give your users access to Plauti Deduplicate is with the Plauti Deduplicate Permission Set. The advantage of using the Plauti Deduplicate Permission Set is that it is updated automatically whenever new classes, tabs etc are added to Plauti Deduplicate. This means you don't have to make any changes after future Plauti Deduplicate updates where new classes might be introduced.
However, with the Plauti Deduplicate Permission Set users have access to all of Plauti Deduplicate, including the settings in Deduplicate Setup. If needed you can deny your users access to certain Plauti Deduplicate pages.
Profile settings, custom permissions
Another option is to grant your users user access via profile settings or a custom permission set. Note that profile settings and custom permissions need to be updated manually whenever a new class, tab etc. is added to Plauti Deduplicate.
If, upon installation of Plauti Deduplicate, you chose to install for Administrators only, all access to Plauti Deduplicate Apex Classes, Plauti Deduplicate Objects etc. was added to the standard 'System Adminstrator' profile. This means that if a new Plauti Deduplicate release contains new classes, tabs etc, the System Administrator profile needs to be given access to those. New classes, tabs etc. are listed in the Release Notes.
Profiles and permissions in Salesforce
Users can have only one profile but, depending on the Salesforce edition, they can have multiple permission sets. You can assign permission sets to various types of users, regardless of their profiles. See Salesforce's 'Manage Data Access' page for more information about profiles and permission sets in Salesforce.