SQLServer 2016

I want to restore to another instance the files from a user database.  I have 4 .dat files for the data and one for the transaction log:

Righ-click on the target database and choose "restore database":

 

 

In the "General" page, choose "Device" and click on the 3-dot button to go to your dat files.  Make sure you select "all files" from the drop-down list so you can see them:

 

Choose the 4 files for the data of your source database:

 

Click on the "Contents" button to check the contents of any of those 4 files:

they should all mention the source database and that it was a "Full" backup.

 

Make sure you select the destination database in this drop-down list, as it will first bear the name of the source database (here I'm restoring P1 to F1):

 

In the "Options" tab, choose "with REPLACE":

 

Click on OK to launch the restoration.  A progress bar is displayed at the top of the window:

It should finish with a pop-up window like this one: