Well, if you mean you want to create a character on a device, you can draw them on paper and then you can copy them on to a drawing app. (I use IbisPaint, but other artists such as KJD or Gemcrust probably use a better app)
You can just draw the character on the drawing app to start with.
But if you want to ANIMATE a character... that's a different story. I wouldn't know how exactly you do it but I hear it's kind of complicated because you have to draw and color in all the different frames, then add the audio, then string them together, and that's all done on a different animation app. To animate, KJD uses ToonBoom Animation Pro.