What size of computer laptop screens are good or ok for graphics,films and surfi

I think the more the size the more will be the visual effects. However a 13" laptop is just fine for all type of purposes. you will never get disappointed with it.

I wouldn't recommend a laptop or TFT screen for graphics at all, no matter what the size. An 'old' CRT monitor gives far better colour rendition. For typing, spreadsheets and such any screen will do. The problem with TFT screens is they need to run at their native resolution. If you run them at less resolution because you want to have bigger text then the quality of the picture goes down quite obviously. So if you prefer a resolution of 1024 x 768 then you must use a TFT screen no bigger than about 15". A 17" TFT runs at 1280 x 1024 and my 20" widescreen I use now has a native resolution of 1680 x 1050 pixels. I'm sure you will get used to your 13" screen. I worked for years on a mono 12" CRT screen!

The screen size doesn matter so much, but somethinf large, say 18-21 inches will make work less straining on your computer screen.

I think it doesn't matter on the screen. If it has HD support then that matters. If you mean a good size for you to see things clearly opt for a bigger screen. Try a 17 inch. But really, I don't think it depends on the size. Oh, but it affects your visuals. If the screen is bigger, you can see it better.