In Ubuntu, there are two ways to install software without using the package manager or a network connection:
.deb is most similar to something like a macOS .dmg or a Windows .exe with a wizard.
While increasing common, they are often not available for more sure software. Use this to install from a local file.
There are also what is known as tarballs. These end in .tar.gz, .tgz. or sometimes tar.bz2. Think of theses as zip files or archives like .7z or .zip. Except in Ubuntu and Linux in general these do not have an installer inside that you run after extraction.
Instead tarballs contain source code that must be compiled. This is an art in of itself and differs per software. This a whole other question. I recommend avoiding this method for now.
So to install software without the internet or a package manager, find and run a .deb installer on the target machine. Find .deb versions on the alternate download pages for the software in question. Load those on the target computer and run the installer. (this can be done using UI or running "sudo dpkg -I' [pathandfilename]" in terminal). Or learn to compile tarballs, and compile on the target machine.
Forgot to mention that these files must be should be moved from the thumb to the main drive for the default installer to work properly. There are others but this is simplest.