Although your professors might have impressive credentials, they're teaching because they want to educate and inspire the next generation of students. Take the first step and approach them; you'll be glad you did.
Sit in the front half of the classroom, raise your hand sometimes, talk to faculty after class, and attend out-of-class opportunities offered.
The more instructors know who you are, the easier it will be to ask them for help when you're confused, and eventually for a letter of recommendation.
It gives you a great opportunity to ask in-depth questions and explore points of confusion or interest that cannot be fully addressed in class. If you're not sure what to talk about, start by asking how your professor became interested in his or her subject of expertise.
Some of your most eye-opening learning will happen through doing research, working in a lab, completing an internship, or studying abroad. All of these give you the chance to work with faculty in new and different ways that will enhance what you've learned in classes.