Make a rough sketch of whatever it is you want to draw, and make it as rough as you want. Afterwards, add another layer above the rough sketch and use thicker lines (around 5 or 6 pixels) to create the lineart. If you think the lines are too wiggly, use stabilizers to automatically straighten them out. For coloring, add a third layer and place it under the lineart layer, and color using the fill and brushes. If you are just starting out, wait to shade your digital art until you are better at creating digital art.