Why dpkg is used ?

to do a configuring of all unconfigured packages if there has been a problem with an update and some packages' configuration is still pending:

sudo dpkg --configure -a

For a great tutorial that focuses on dpkg and apt-get, see chapters 5 and 6 of the Debian Handbook

Resource Link: https://askubuntu.com/questions/173465/what-is-dpkg-for