One way to create a useful image of the chymotrypsin active site involves the issuing the following command into the command line:
hide
create inhi, chain d show sticks, inhi show sphere, inhi color forest, inhi
create active, (resi 57,195,102) show sticks, active color marine, active
create protein, (chain a,b,c) show surface, protein color gray, protein
set transparency, 0.27 set sphere_scale, 0.17 set stick_radius, 0.15
Next, rotate and zoom the structure into a position that best illustrates what you want to show. Finally, you may raytrace the image with the command ray to provide a more photorealistic look and save it as a PNG file on your hard disk.
A gallery of PyMOL images with associated PDB files and scripts (you can run these in PyMOL from File > Run) is available at http://www.chem.ucsb.edu/~molvisual. You may want to examine this collection of images. If you see something that looks interesting, read the script file with a text editor to see what commands were used to create these images. Note that most files there are several years old and do not reflect the best capabilities of PyMOL. Feel free to ask my help in understanding these files.