Direct commands
Program lines can be typed in with a line number and will be accepted and stored for later as part of a program. However, if you type a line with no line number, it will be executed immediately. This is a "Direct Command". You can also use the editor as a simple calculator - type in an expression, such as 2+3/(4-2) and press Return. The result will be displayed in the display area.
All direct commands are "logged" in the Command History Window where they can be re-called for repeated use.
When the command has terminated, or the expression has been evaluated, then usually a "0 Ok" message dialog will appear, indicating that all went well. Closing the "Error Message" dialog will return you to the editor.