RPM (Red Hat Package Manager) is a package management system.
The .rpm files are used primarily by distributions that derive from Redhat based distros (Fedora, CentOS, RHEL)
The .deb files are meant for distributions of Linux that derive from Debian eg Ubuntu, Linux Mint, etc
To Convert a .rpm installation file to .deb use Alien.
Alien is a program that converts between the different Linux packages.
To install Alien, run the following command
sudo apt-get install alien
After a successful install, now run the command that will convert your .rpm package.
sudo alien my_package.rpm
And with that, you have your .deb package.
Install it using the following command
sudo dpkg -i my_package.deb