In order to run specific *Commands or use certain command-line only applications such as RSync or OpenSSH, you must enter the RISC OS command line. This can be achieved by clicking the menu button on the RISC OS (or Raspberry Pi) cog in the bottom right of your screen and selecting the Task Window.
Alternatively, you can access it by pressing F12 on the desktop, this will open up a command line interface on the bottom of the screen. Pressing enter twice will exit the interface.pressing F12, this will open up a white command line box at the bottom of the RISC OS desktop.
Once you’re on the command line, you can run programs by typing the name of the command-line application you wish to run then press enter.
To exit the RISC OS command line at any time, press enter twice in quick succession.
For more information on *Commands on RISC OS – have a read of this.