Here are my tips to get the hang of writing under a CCTV:

Go into the Photo Mode of your CCTV
Take magnification down to its lowest setting, at least to start
Get a black-inked pen. A medium or fine point roller ball or felt tip pen works great
Put pen in hand on top of writing paper (lined paper is good for practice) under the CCTV camera, on the XY tray, if your device has one
Watch the screen, not your hand. Move your hand around until you see your hand holding the pen on the screen
Touch pen to paper until you feel the contact
Watch the screen, not your hand, and start to write
With your other hand enlarge the magnification until you can see your writing as you are laying that ink down. Keep your eyes on the screen.
You may find you need to slide your hand/pen/paper horizontally as you write to keep the words on the screen as you are writing them. People using an XY tray leave the tray unlocked so the tray moves with your writing; others lock the CCTV tray and slide the paper on their own.
Now get comfortable. Have your elbow in or out. Paper lines can be parallel or at an angle to the screen edges. It doesn’t matter. Just find a position that is comfortable. Watch the screen; doodle, draw, or just enjoy your penmanship! It is actually fun.