Install the Chrome extension, add the people you genuinely know as trusted connections, and start making introductions. That is the whole loop. Training videos on the home page walk through setting up your network and getting the most from each introduction.
You can only add people you actually know, one at a time. There is no bulk import and no cold outreach to strangers, so a request always travels through somebody who can vouch for you. That constraint is the product rather than a limitation of it.
Download the Chrome extension. What Premium adds. Ask a question.