There is an art to sketching fast as Gillian has shown and it comes with loads and loads of practice.
Often an artist will use these quick sketches to develop a more substantial work.
have to say I work very very slowly and have not mastered what Gillian has just shown you but its just picking up the basic details of a cat. Cats are also not good models unless they are asleep LOL.
I tend to use a photograph or photographs and Zephyr who I have in the gallery tooks me between 3 and 6 months to do with a couple of hours work at the most for some weeks, But also he is quite big in that its on A3 paper and been done with a lot of detail all in pencil.
Timothy however is even bigger and is in pastel but only took about 20 hrs plus spread out over a couple of months.
I have never done anything on the computer and dont think I would.
I think what you need to do is get some pictures of cats to start with or use your cat and/or photos and just keep trying to produce an outline likeness. The other alternative is to join a class to learn to draw, hopefully with a very good and symapthetic teacher. Cos it doesnt matter what you learn to draw this will help you to draw cats.
Thats what I did for a year, three years ago, and it started with an apple lol and covered pencil, ink, pastel, pen and wash. I never did a cat the whole time but I did do the wolf which is in the gallery and is pastel on black paper. It was done from another art work, although not a true copy but I had only been drawing for about 15 weeks doing 2 hrs a week!
Good luck and love to see how you progress.
Misa was done much quicker but is just a basic outline really and taken from a photo and I think I did do it as part of my course cos we were touching on texture and was after the wolf , nearly at the end....the others do=id things like brushes and feathers but I had to be different LOL