In general, I'd recommend using
dpkg -i, as waltinator wrote and it's the safe and sane method.
However, if you have a vary large number of packages, and you wish to easily manage installing and uninstalling them, with dependency management, the following should work:
sudo apt-get -o dir::cache::archives=/path/to/directory/containing/archives/ -o dir::state::lists=/path/to/directory/containing/lists --no-download install your-packages
In order for dependency management etc. to work properly, you may need to copy the package metadata (normally present at
/path/to/directory/containing/lists on the offline computer.
You could also just copy the packages and the lists directly into the default directories
/var/lib/apt/lists/, respectively, on the offline computer and skip the options part (
-o dir::cache::archives=/path/to/directory/containing/archives/ -o dir::state::lists=/path/to/directory/containing/lists).