There are several problems within the command that you are trying to invoke:
First of all, you must be sure to have root privileges to install new packages with apt-get install.
For this reason you invoke the command with the sudo command:
sudo apt-get install s.th
You can find further detail on root and sudo command on the Ubuntu official Wiki
Do what pkgs ask you
May I suggest you to follow suggestions from dpkg? From the output you posted you can see that dpkg request to execute the command:
sudo dpkg --configure -a
This will purge all the pending packages, and it will restore your system to a clean situation.
After that command I suggest to run even
sudo apt-get update && sudo apt-get upgrade
To force a system update.
From your command I can see that you are trying to setup the package s.th. Please that in consideration that s.th is interpreted by apt-get as a regular expression, and will setup all the packages that match that regexp.