So that you can knead your own figure, you need either modeling clay or polymer clay. I use polymer clay because this clay hardens in the oven.
So that you can start kneading, you first have to put together all the colors that you want to knead with. If you're kneading with polymer clay and your plasticine is hard or crumbling, rub it in your hands until it's warm and it won't crumble anymore.
Now start kneading the figure that you like to make.
If you've used polymer clay for kneading, put it in the oven as described on the package.
Make sure to wash your hands after kneading.
Here are a few more videos from me on the subject.