Many things seem frustrating until you see how they work.

When you say "find a package" are you talking about searching in
synaptic or the software center to find a package in the repositories?
Or did you already download a deb package and you just want to install it?

You can install an existing deb package file either from the file
manager or the command line.

On the command line, type "sudo dpkg -i <name of package file>" to
install it.

Or, if you prefer to use the file manager, just right click on the deb
file you downloaded and you will see an option to install it.

BTW - the firefox that comes with ubuntu has a package manager plugin.
If you are downloading a deb file the firefox plugin will offer to
install the package for you.