Make sure that the deb file doesn't have space in its name or else it may create issues. before the deb file name: sudo apt install. Or, change the directory and be in the same location as the deb file but add.

To install deb files with the apt command, you need to either provide the path of deb file: sudo apt install path_to_deb_file You'll need an active internet connection to download and install the dependencies of course.

Why? Because it installs the deb files with the dependencies. Using apt command to install deb files in the terminal (recommended) I presume that you have already downloaded the deb files here. There are other ways you can use to install deb files in the command line. The apt command is not the only way here. If you are in the same directory as the deb file, you must add. You can use the apt command to install deb packages in the terminal like this: sudo apt install path_to_deb_file

If you download the deb file and want to install it using command line, you can do that easily as well. It may not work if you are running an Ubuntu server and there is no GUI. That works in most cases if you are running it on a desktop. You just have to double-click on it and it gets opened in the Software Center. Installing deb files in Ubuntu is not difficult.

Debian install deb file