Hi
The flashing indicates to me that you have the sync off. This means that the screen is updated after every command, thus the flashing. Before you start coding a game, always perform the following setup commands:
sync on/sync off - If on, the screen will only be updated after you call the command "sync". This allows you to position and calculate objects, or print a lot of different text and shapes to the screen before rendering it. If off, the screen will be updated after every command, which can result in flickering. Only use this if you are making a text adventure.
sync rate - This command will set the "frame rate" of the game. Only use it if you have the sync on. The usual value most games use is 60.
backdrop on/backdrop off - If on, everything from the last render on the screen will be cleared and replaced with the updated render. If off, the screen wont be cleared, which can cause smearing. This is good for text adventure games if you want the text to stay on the screen.
color backdrop - Will color the backdrop to a certain color. Use the "rgb(<red value>,<green value>,<blue value>

".
hide mouse/show mouse - Will hide or show the mouse.
autocam on/autocam off - If on, the camera will lock onto the last object created, if off, the camera will not lock on and stay positioned at the last given positions (default : 0,0,0)
And that's about it. So for a text adventure, you'd use something like:
rem setup screen
sync off
backdrop off
color backdrop rgb(0,0,0)
hide mouse
TheComet