Where is the contacts address list

I am a new user. My contacts list shows empty. But the soft ware will find an address from some source unknown to me. has my former Thunderbird address list been copied or not

If you imported from Thunderbird, then they will probably be in Local Folders.

Make sure Local Folders are enabled by selecting Menu > Settings > General > General > Show Local Folders, then click on Save & Close.

Go to the Contacts section of eM Client and click on the Local Folders contacts folder.