To use just download the .AppImage of your choice from here, make it executible (with GUI or Terminal) and run it.
Terminal example:
chmod +x srb2kart*.AppImage
./srb2kart*.AppImage
Ignore the .zsync files those are for the updating system.
If you download an AppImage without assets make sure you have them somewere else beforehand. In case you do not, they can be found here. Place the .kart, .srb, mdls and mdls.dat files in ~/.srb2kart.