Networking & errors

My company recently had a guy come in & set up a network for our maintenance program. We are having problems with it, so I would like to set up another network & tie the maintenance program to it so that I can work on it. I have no idea of how the guy set it up & don’t know how to fix anything. Can you tell me how to set up a network. We have 4 computers at our job & we want all computers to be able to access this maintenance program. The program is license for 3 computers. Can you help me with this?