To add someone to a list in your network, use the 'Add to List' button (shown in the bottom right of the search result or on their full profile page). Adding someone to a list will automatically add them to your network too.
You'll then have the option to add them to an existing list or create a new one.
Once in your company network, you can use the 'Add to List' button to change the lists a person is included in at any point, and add them to as many as you need to.
Freelancers are not notified when you add them to your network or lists - this is private to your company users with Full access.