You will take two portraits: one on a background of your choosing (inside or outside) and the other on the green screen. Then do the following:
1) Take the 'normal' portait and tweak it to perfection. Play with levels/curves/contrast/highlights/shadows/saturation.
2) Take the 'normal' portrait and make it black and white. There are several ways to do this, all of which will produce different results.
3) Take the green-screen portait and make it pop-art.
4) Take either portrait and use artistic effects to change it radically. See my samples.
For all of the above Google can be your friend. For example, for #2 I would search the following string:
"photoshop how do i make a photo black and white?"
Youtube tutorials can be the best way to learn.