Hi and welcome to Fedora!
When asking questions it may be beneficial to specify what you’re using (Workstation, Silverblue, KDE, Kinoite etc), since UI and performing certain activities may vary a bit 
In general, Fedora is using dnf, which is an rpm-based software. Installing .deb files isn’t possible on Fedora nor derivatives. You can (generally) install only rpm files and flatpaks (like from Flathub or Fedora remote). In the case of rpm packages, assuming you’re using Workstation or KDE, just click on the file and it should take you to the App Centre. You can install it from there.
Hope this helps!