The People panel has tabs to show who's nearby, your Friends list, and pending Friend requests. You can open the People panel by choosing Socialize > Friends & People from the main menu.
Nearby - This tab lists all nearby people in your current experience. For each person on the list, you may click their name and choose to Message them to send a private message as described above, or you may Add Friend to request a mutual friendship. The other person must first accept your Friend request before they appear on your Friends list. You can also Send Gift to send them Sansar dollars. Additionally, you may choose to open that person's user profile, which contains additional muting, friendship, and reporting controls.
Friends - This displays a list of your Friends, regardless of whether they are online or in your current experience. For each person on the list, you may click their name to either Message them, Send Gift to send them Sansar dollars, or open their user profile, which contains friendship and communication options.
Requests - Shows a list of currently pending Friend requests you have received from other people. For each pending request, you may click the person's name and then press Accept to accept the request.
Search - Enter part or all of someone's Avatar Name or ID and press the Search button to return a list of matching results. You may click the resulting name to reveal options to Message, Friend, Send Gift, or open the Profile of that person (which includes messaging, friendship, muting, and reporting options).