Those files are special Data files that contain the info needed to directly add a server as connection in your MineBuddy app they are harmless plain INI documents with certain structure. (can be viewed using text editor)
Importing is easy and can be done in 2 ways.
The easy way simply doubleclick the MBSD file and the app should open and import.
If step 1 fails or u wanna do it manually go to the server manager and click import. then select the MBSD file
Go to the server manager.
Select the server you wanna export
click export server
Select a location to save
And voila its done!