That's a easy job...
first decide that wht u want to use ur linux ... as sever or as client.
If server then u can use dhcpd ,proxy , nfs, samba and various other servers to share file on ur LAN.
If as client.. just configure ur eth0 go get ip address from dhcp if u r having dhcpd server on lan otherwise give a static one.
Now to share files on ur lan .. i suggest samba.. as it works best in heterogenous networks.
And to connect to internet.. u have to first tell us that wht type of connection u r having .. is it simple dialup, ISDN, Cable or wht??
Now give us ur detail .. wht u exactly wanna do?