The best way to get started is to use free software. My favorite is Microsoft NetMeeting 2.0. MS Internet explorer 3.x includes NetMeeting, version 1.0. However, NetMeeting can be used independently of browsers, and does not interfere with them. It is available on the Microsoft Site and the file is about 2.6 Megs.
Installation is automatic as is calibration of the microphone.
This makes it ideal to discuss a problem with a document or spreadsheet as two users can access the same one. This is like CB, when one person speaks at a time. It is not like the telephone. Unless the program is active and you are connected to the Internet, callers cannot reach you. While up to six persons can be connected at one time, only two of them can chat by voice with each other.