Summarize the following:
Once you've got all the molding installed, use caulk to fill any gaps at the corners and other gaps. Be aware, however, that if there are gaps between the molding and your baseboards, you may have simply placed your nails too far apart and adding an intermediate nail may help. Use a nail crayon, if you want to, to fill in the holes created when you countersunk the nails. With everything else done, all that remains is to stain or paint the molding however you want it to look. This is easiest when the baseboards are also unfinished, but if your baseboards are already stained you might want to stain the molding before installing it. Once your paint or stain is dry, you're all done! Enjoy your new, professional-looking room!

Summary:
Caulk gaps to create a smoother look. Use a nail crayon to cover the nails. Paint or stain your molding.