Grades open doors for you. Talent, attitude and determination allow you to walk through.
Below are some resources for playing college baseball.
The Athletic
Recruiting and Scholarship Guide

The Top 96 Showcase is one in which you can show your skills to college coaches. The showcase in Massachusetts is invite only. Most of the other showcases will list the colleges that are attending. If you see a coach from a school that you are interested in attending it is in your best interest to attend.
The NCAA Clearinghouse is one in which you need to visit. The site provides information for the prospective college athlete. Athletes must register with the NCAA Clearinghouse in order to play college athletics.
"Showcase Expectations" provides detailed information on the showcase experience and how you should prepare for it.
"A Road Map for College Baseball" is a must read for anyone that wants to play college ball.