Its not really difficult to learn how to sketch on a Graphic tablet but keep in mind that it is much better to sketch on paper first, scan the outline of your sketch and then post-process / color your outlines using Photoshop / CorelDraw or any other tool of your choice.
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Ruba Nesly , Page Manager & Content Creator for Emirates Loves Syria Page , New Media Academy
It is nice idea to practice drawing using graphic tablets, but also it is enjoyable to use the classic method in drawing, plane paper and sharp pencil is the most attractive tools for an artist to start drawing, learn how to draw. Good Luck Salma :)