The following was tested on Ubuntu 18:
1. Open a terminal
2. Check whether Java is already installed. Type:
3. If Java is already installed, skip to 4 below. If not, install java. Type:
sudo apt install default-jre
This installs the Java Runtime Environment for the version of OpenJDK that was packaged with Ubuntu. On Ubutnu 18, this is either Java 11 (after September 2018) or Java 10 (before).
When installing, answer Yes when asked if want to continue as additional disk space will be used.
4. Download the zipped archive for Orinj version 4 from this site.
5. Unzip it. Preferably, unzip Orinj somewhere in your home directory or in a subdirectory, as Orinj may want to write files inside the folders of its own installation (e.g., when saving effect presets).
6. Make the orinj.jar file executable. In the terminal, switch to the "orinj" directory of the Orinj installation and type:
chmod +x orange.jar
After the above, double click on orinj.jar to run Orinj.