As a new Ubuntu user I installed the OS by downloading the software via terminal commands without problems. Now I would like to install additional software packages. While trying to install downloaded packages via terminal I get errors. Please help me to install the downloaded Debian packages with terminal commands and please address possible repository dependencies.
The reason for not installing software from online repositories is that this produces reasonable internet traffic that cost me a lot. Therefore it would be good to find a way to install software packages without the need to download them each time.