Many recruiters make extensive use of LinkedIn. The platform is designed to help you get your name out there and find a new job. You can open an account for free, then set up your profile page by adding information about your education, work experience, and skills.  Keep the information and language on your LinkedIn profile professional. Use a picture of yourself in which you are well-groomed and professionally attired. If you have a recent school photo or graduation photo, that may work. Take a moment to search for people on LinkedIn you might know, but keep in mind that LinkedIn is not a "social" network like Facebook or Instagram. Just because you're friends with someone doesn't mean they'll necessarily add value to your network. On the other hand, connecting with former teachers, bosses, or coworkers is always a good idea. The recruiter's business card may have an address for their LinkedIn page on it. If not, you can use the LinkedIn search function to find them. Simply type their name into the search bar. When you find the profile for the right person, look over it briefly to get some more insight into that recruiter's career history and their work at the company. You may find other things you have in common with the recruiter. For example, they might have graduated from the same school as you. Type a brief 2 or 3 sentence message mentioning that you met them at the career fair and would like to connect with them. Mention the name of the career fair specifically, along with the date it took place. You might also include detail about something you talked about to help the recruiter place you.  For example, you might write "Hi Ronda Recruiter! We chatted at the Unicorn University Career Fair on April 1. I'd like to connect with you here to keep up-to-date with any opportunities that may open up in your organization. Thanks!" If you simply send a request to connect without a message, the recruiter likely won't accept your request. Most LinkedIn users don't accept connection requests from people they don't...

TL;DR in Chinese:
如果你还没有领英（LinkedIn）账户，那就注册一个吧。 在领英上搜索招聘人员。 发送一条简短的消息和联系请求。 使用领英关注你感兴趣的公司。