You're receiving a lot of great advice here. A couple of additional thoughts:
While I couldn't agree more with the advice that you can quickly become a valuable resource for your son by immersing yourself in the information available on this site, never lose sight of the fact that your son needs to be at the forefront of his recruitment.
You are not his agent. It's his gig.
It's his passion that fuels his work ethic to improve as a player. He needs to harness and channel some of that same energy by taking a direct role in determining where he ends up after high school.
Some ongoing steps he can take? (1) Researching schools. There's a wealth of online information about college characteristics that he's capable of digging up. (2) Communications with coaches. This takes a variety of forms and becomes more involved as NCAA regs loosen with his advancing age and programs become genuinely interested in him. However, in the early stages, he should be the one sending emails, returning questionnaires, etc.
A significant additional responsibility of his is to perform sufficiently well in the classroom that he qualifies for admission to his chosen schools, This goes for college entrance exams, as well. As a rule, baseball coaches are limited in their ability to grease the skids for subpar students. One of the biggest favors your son can do for himself is keep his college coach out of the Admissions Office; pleading on bent knee on his behalf.
With your son at the lead of his recruitment, you'll see an amazing maturation process take place; one that will serve him well in a number of important respects and not be lost on the coaches whose impression counts for so much.
Best of luck to him!