Before you can start tackling duplicate records, there are a few settings to configure. Follow the checklist below; once finished you're ready to go! 

☐ Start with downloading and installing Duplicate Check for Dynamics 365.

Once installed,

☐ Configure your apps to work correctly with DC for Dynamics 365.
Make sure Asynchronous Form Handlers are enabled for all apps where you want to use Duplicate Check. Without this Duplicate Check will not work!

☐ Grant permissions‍ if needed, and check users' record permissions.

Then, configure Duplicate Check for Dynamics 365 to prevent duplicates the way you want to.

☐ Create Scenarios‍ to determine when two records are considered duplicates.

☐ Configure at which moments Duplicate Prevention‍ should take place, and whether it should only alert for potential duplicates, or also block creating duplicates.

Read more about setting up Duplicate Check for Dynamics 365 here‍. 

Once you ticked all the boxes above, you can start preventing those duplicate records from being created. 

So, with everything set up, what does it actually look like when you are about to create a duplicate? Read more in Preventing Duplicates upon Save and Preventing Duplicates As-you-type. 

And how can you clean up your existing records? These articles about finding‍ and merging‍ duplicate records tell you more.
Finding duplicates with Duplicate Check‍
Merging duplicate records‍ 

Furthermore, have a look at this video: