It depends on your wifi router. Your master control on the internet connection depends on your router. Normally this can be accessed through 192.168.0.1 then it will prompt you for a user and password. I believe you cannot pause the connection but you can prohibit that computer from getting an internet connection. You just have to know the IP address.
On the other hand, once two or more computers connects in a single router, they computers are already in a network and their IP's are assigned based on the router settings. But access to files are other stuffs is just another thing.