Computer networks can fall into three broad categories--local area networks (LAN), microcomputer based messaging systems (this includes computer bulletin board systems), or commercial information systems. Many of the same types of activities take place within the three categories. The major differences are the types of information available and the way in which access to the information is provided. This digest is primarily concerned with microcomputer based messaging systems but it distinguishes this type of network from the other two. The digest comprises sections on: what networking is; local area networks; commercial information systems; microcomputer based systems; user requirements; getting started; services available; trouble shooting; and resources. (THC)