WHEN I TRY TO DRAW SOMETHING ON 3D MODE,THE PROGRAM SEND A MESSAGE ALERT "THE PAPER IS NOT VALID TO MODEL"
The sheet needs to have an indication of which direction each part of the drawing is viewing, like the traditional note of whether a drawing is "1st Angle" or "3rd Angle". To do this, and to add non-orthogonal views if needed, Medusa requires a boxes on the sheet of type LVB which enclose the drawing and a small "prim", known as a "view-prim". That's the funny little block which looks different from each direction. (*)
draw the boxes and add the view-prims yourself, but the easy way is to switch to 3D mode before starting a new drawing. The menu of new sheets will then have suitable boxes already drawn, with viewprims (in 3rd Angle) and some centrelines to help construction.
ABOUT THE LICENCE,WHEN I OPEN THE WINDOW AT THE TOP INTHE RIGHT SIDE(NEAR HELP) EVERY LINE IN THE WINDOW IS DISABLED LIKE "RASTER ETCCC..."
The licence you have is printed in the text (command) window behind the drawing window. That's on Linux anyway, I have no idea what happens in Microsoft.
(*) In the early days of Medusa each customer was given one made of wood with a felt base, for each workstation.