Do you mean associating filetypes from Windows so they open in calibre?
calibre automatically registers filetype associations on Windows 8 and above.
You can manually associate them on Windows 7 by entering the following into a command prompt:
Code:
calibre-debug --default-programs=register
Note that this will automatically set calibre as the default for filetype that does not yet have a default -- this may not be desired, since calibre handles a variety of files including DOC/DOCX/ZIP/RAR/TXT/HTML/PDF.