For starters you need to draw something…it needs to be only line art with no shading or details. Bring me the line art to be scanned. OR use the WACOM tablet to trace an existing drawing that you download!
Once you have drawn your line art, clean it up so that all that remains are the lines you want. Erase any stray marks or lines before we scan the drawing. Once it is ready to be opened in Photoshop it may still be messy and need to be cleaned up or drawn on, like this:
Now choose Image – Adjustments – Brightness/Contrast and slide the slider to the right first on the Brightness levels, then on the Contrast so that the white of the background gets bright and clean, and your lines get darker and stronger.
Once your drawing is cleaned up it should look something like this:
Now that your drawing is cleaner, click on the background layer to unlock it- call it Line Art and change the Layer Mode to Multiply. Create a new layer underneath this Line Art layer, name it background and fill it with white by choosing Edit- Fill – White or choosing the Paint Bucket Tool (G), select the color white and clicking anywhere on the new background layer.
Switch to the Brush tool (B) and begin experimenting with all of the brushes that are available to you.
Once the Brush menu is open, click on the small triangle in the upper right-hand corner to add to your list of available brushes. When choosing a new brush list, click on “append” to your list so that you do not lose the existing brushes.
After all your selections are saved, all your new layers have been painted, paint your background. That original white layer will now be used to create some kind of environment for your subject to live in.
Here is a good example of the whole process: First find a good line drawing!

Start with some good Line Art (no shading or color allowed)
Now select, create a new layer, then paint each part onto ITS OWN LAYER.

Add color using the Paint Bucket Tool
Now shade the drawing with a soft airbrush (the Brush Tool).

Shading added and background painted!
Save this painting as P01LastFirst as a PSD so I can see your layers and grade your drawing and shading skills. Turn it in to your Google Classroom for me to grade it. It is worth 100 points.
More examples of finished works…

learn how at :
https://tutsplus.com/tutorial/iron-man-fan-art/