How do you network throughout college with people that can help you obtain a job after graduation?
Join pre-professional organizations.
Try to get summer internships.
If you're able, seek out internship opportunities. Sometimes faculty members can pass along internship information, your college's Career Services Office can assist, another possibility is to review the websites of companies you're curious about. They sometimes post internship offerings on their career opportunities webpage. If your schedule allows, you can pursue internships during the academic year (sometimes for course credit) as well as during the summer. This is a great way to gain insights into a company / organization. It also provides you with a chance to develop and expand your professional network. Internships can sometimes lead to permanent, full-time career opportunities.
A second professional network to tap includes your college Alumni Association. See if you can volunteer some time with this office/association. They sometimes sponsor gatherings with currently enrolled students. This is yet another way to develop your professional networking skills.
Finally, some college Career Services Offices have a listing of alumni who students can contact for career / professional advice. For example, you may find an alum who works in a profession or for a company that you're interested in. It's an ideal way to gather "insider" information. If you continue to nurture the relationship, you may become privy to internship and/or professional positions.
Hope this helps!