put simply when you F6 it means that at any point in the program you can press escapekey then look at the values in your code to see what they store or if they are storing the value you think they should. plus to can direct command input so say there a cube on the screen you can say position object id x,y,z and change any of the value for a id x y z to move that object, can also be done with say color object id new rgb values, you see it change color there and then.
hope that explains it a bit more.
Dark Physics makes any hot drink go cold.