To add friends to your profile, you have to find them first. This can be accomplished in a couple of different ways.
First sign-in...then search
Once you locate them, click "Add as Connection" button in the upper right corner of their profile.
A request window will pop-up. You can add more information to your request or send the standard request to that person.
The friend will receive an email with the request and can accept of decline the request.
Once the friend has accepted your request, you can have private conversations and keep track of their activity.