You should login as a normal user rather than as the superuser (user Root).
If necessary, you can switch user to Root from a normal user's account. using the switch user (su) command. You need Root's password for this.
There are several applications that install Debian packages. synaptic is an X Window System progam and aptitude is an ncurses program which runs on a terminal or in a terminal window in X. apt runs from the command line. The examples in this document use apt.
Use apt to install a package.
# apt-get install package-name
Use apt to remove a package.
# apt-get remove package-name