Before LinkedIn was developed (and even today), anyone who posted their resume on a job board risked someone at their current company finding out. With a robust LinkedIn profile, you have the opportunity of being approached about a tremendous job opportunity without it being apparent to your company that you would consider other options.
LinkedIn makes it very easy to develop your profile everything from your experience, education, skills & endorsements, publications, and recommendations. You can also attach documents such as your resume.
If you don't have a LinkedIn profile, develop one as soon as you can. If you have an existing profile, take the time to update it.