. deb files are for debian systems and shouldn’t really be installed on arch based distro, I think its possible but very difficult.
If you are new to manjaro then use the pamac gui (add and remove software option) to search for and install programs. If the deb file program isn’t in the official repos then its more than likely available in the AUR, flatpak or snap options in pamac.
In MANJARO and ARCH based distributions have script to convert .deb packages to Arch Linux package ----- the name is “debtap” . You can find it in the AUR repositories.
READ this: How to Install Deb Package in Arch Linux - Make Tech Easier
I think that telling a newcomer to the OS, who does not know that in Arch-based systems .deb files are not normally the first choice for installation of packages, about debtap is not advisable.
OP, please consider sawdoctor’s post and also please read up more about the OS that you are now using.
Please, please, please don’t follow @stoner’s advice and follow @sawdoctor’s and just tell us what it is you want to install. We’ll help you!
@stoner I agree with @wongs that although your answer is 100% correct, it’s also 95% dangerous if @chump114 is new to Linux in general and 90% dangerous if he’s used to Linux but new to Arch-based distros…