Appearing online on Steam lets other users see that you are currently active and available to interact with. This can be useful for finding friends to play games with, joining groups, or simply showing others that you are online.
To appear online on Steam, simply launch the Steam client and log in to your account. Once you are logged in, your status will automatically be set to “Online”. You can also change your status to “Away” or “Invisible” if you do not want to be disturbed.