Ultimately, the responsibility for finding your first "job" lies with you. There are a lot of different avenues to success in landing that job and a college placement service is just one of them; an important one, but not the sole avenue to success. When you enter college, you will (or I hope you will) begin building relationships and networks within your academic circles, possibly leading to internships or work with professionals who can help you network and expose you to career opportunities. Those are at least as likely to lead to your first real lead than anything, but (again) only one of many sources you need to look into.
Will your college placement office play a big part in this for you? Hard to say, as I'd venture to guess that success is defined differently by each individual office and the results vary widely. But they usually have internship postings, actual job postings, information about interviewing and company/organization contacts or information. Plus you've paid for it already. Take advantage of it as best suits your situation.
And you may also end up having to do some of your own networking, applying for positions, interviewing, finding your own internships, etc. Remember, it's YOUR career and you own it. See something interesting in your field? Write to people working in that specific arena and note your curiosity. Look up profiles of people who are doing what you want to do on LinkedIn (for example...) and see how they got to where they wanted to go. Check the career paths of graduates of your college and seek their advice or see if you can find a similar job for that first berth. Almost everyone is anxious to talk about themselves or their passions and share it with other devotees.
Don't assume it will be easy, as it may end up being hard work (and a bit frustrating at times). Keep at it and be persistent.