The DEB file extension identifies standard Unix installation archives for Debian-based Linux distributions. Deb files contain several bzip, gzip, or LZMA compressed archives. In addition to the actual program data, a DEB file also contains information about installation and dependencies.
In addition to the normal installation packages, so-called binary packages, there are also source packages containing uncoiled program data, the source text. Source packages are not easy to install, but must be converted to a binary package by compiling the source code.
Deb files are generally only installed on Debian-based systems. If a DEB file is executable (has the appropriate rights), it can be started and installed by double-clicking. They are not compatible with rpm packages (another Linux installation format), but can be converted with the alien program. It should be noted that, of course, the underlying architecture must remain the same. (a 64bit program only runs on a 64 bit operating system)
If you want to look into DEB files, a file manager such as the Konqueror or Midnight Commander is usually enough.