joe213 I could, or I could just link you to the website. It should have everything you need to know there. I'd also recommend looking into symlinks (symbolic links) and .desktop files. .desktop files are the main things you use to start applications (they're what shows up in your application menu).
You'll want to create symlinks to firejail with the name of the application you want to run in a directory that your environment looks in first. Typically, something like this to set up a working symlink
sudo ln -s /usr/bin/firejail /usr/local/bin/steam
sudo ln -s /usr/bin/firejail /usr/local/bin/firefox-esr
That's for Steam and Firefox-ESR. I think some repositories have Steam called
steam-launcher instead. Then you just want to make sure your .desktop files point to "steam" or "/usr/local/bin/steam". There's an Exec line that you want to look like:
After that, you can run the application like you normally would. If it's just for your own user profile, I'd recommend using
menulibre for altering the .desktop files. It will just write a new .desktop file in your personal applications directory and hide the original system one. That way when the package gets upgraded, it won't overwrite the new file.