To test the program : download the whole depository, extract it and launch the .exe
Commands : right-click -> move the camera | drag left-click -> select bodies | space -> pause/unpause | n -> add a new body.
You can change the properties of each body in real time, but it's easier to do it under pause.
You can change the timeStep with the first cursor in the top right-hand corner and change the size of previsualisation with the second one.