I use the freebie version. It's like Professional Facebook. To be most effective, build your network over time and link to people at or above your "level" in your circles. Get active on the Q&A part and answer questions to become known as an "expert." You can also use it to search for particular positions in other companies and find out who has that job. This is good if you are trying to get beyond the "gatekeeper" who answers the phone or an email/po box response point for a listed opening. Once you have someone's name you can then contact them through LinkedIn and become something more than an anonymous job ad respondent. You're a person. Good luck.
Ron
Oh, remember that when you post updates on LinkedIn or Facebook everyone you're linked to gets the update. Be careful with what you say.