If you have not already created an account and joined LinkedIn you need to. http://www.linkedin.com/ Its Free.
When you join LinkedIn, you create a profile that summarizes your professional accomplishments. Your profile helps you find and be found by colleagues, clients, and partners. You add trusted contacts to your LinkedIn network and in turn have the ability to be networked with your connections trusted contacts.
LinkedIn organizes people by degrees of separation. So people that you know (directly) are in your network 1st degree, people they know are in the 2nd Degree, and so on.
Through your network (and extended network), you can find potential clients, service providers, subject experts, and partners who come recommended. You can search for jobs and get introduced to other professionals through the people they know.
Lets say that you have created such a profile and you are looking for someone to help you build a web site. You can then search LinkedIn for web developers and a list of people you know will appear who match that criteria (1st Degree) and the people they know (2nd Degree). You can then contact that person through the person you know.
LinkedIn offers a pay service which allows you to connect with people who are in the 3rd degree of separation from you. I have never used the pay features of the site.
I use LinkedIn to find contacts at companies and people I want to network with. Commonly, if I have a sales opportunity with a company, I will search LinkedIn to see what contacts in my network have contacts at the company I would like to do business with.
This is also a great tool for people who are job hunting or looking for employees. If you have an interview somewhere, you can search for contacts that work at the company you are interviewing with and see if anyone you knows someone who works there. If you are looking to hire someone for a job you can search by those skill sets and find potential employees.
In this day and age networking and marketing through referrals is the best way to contact others. LinkedIn allows you to do that by organizing and linking the people you know to people they know. It is very easy to use and will change they way you use and stay in touch with your contacts.
To learn more about LinkedIn visit their help center: http://LinkedIn.custhelp.com
Also, check out the LinkedIn Blog: http://blog.linkedin.com/
Can you view my LinkedIN profile here: http://www.linkedin.com/in/ericclemens