Promble of connecting two or more system

Hello,
i want to make a connect of six system through a modem ,i try get a d link modem and install one system as the server and the other to share from the main system i could ping the ip of the system but i can still connect the internet from the other system i could only connect the to internet from the main system which the the modem is but the are seen each other but still not connect to the internet what should i do