LinkedIn allows you to crawl through other profiles that may allow you to find other contacts that you can connect to.

If you click on the "Add Connections" in the top right hand of the "Contacts" tab, you can search your email for contacts:

You can also remove a contact from your network by clicking on the "Remove Contact" in the top right.

The reason you want to add contacts to LinkedIn other than to grow the size of your network and solidify your authority is that it allows you to export their email addresses. You should always have their permission to add them to a mailing list and never spam them.

From the main "Contacts" tab, you'll notice a blue "Export Contacts" at the bottom of the page. This will lead you to the following menu where you should choose to export the information as a CSV (a format which is recognized by most if not all good newsletter clients).