If you are not using a local router then you probably need to get the correct settings from your ISP. They will probably have you use DHCP.
If you are in a workplace setting with IT people in charge of the network, they can help you. They might have you use DHCP.
IP Address: If you are assigning a specific address (static IP address), then you should know what addresses are available. If you are using DHCP then you don't need to fill in this field.
Assuming that you are not using DHCP, when you fill in the IP address the network tool will fill in some default, but not necessarily correct, guesses for some of the other fields.
On my home network, my router is at 192.168.0.1 (which is a common default address for a home router. Sometimes you see 192.168.1.1 or 10.0.something.) so I use addresses in the range 192.168.0.xxx. On my desktop system, I use 192.168.0.96 and the network setup tool fills in (I'm doing this from memory so it may not be completely accurate but should give you the idea):
network mask 255.255.255.0
broadcast 192.168.0.255
and
gateway 192.168.0.254
The gateway default is wrong in my case and I suspect it is wrong for the majority of home users with local routers. I always have to change it to 192.168.0.1 which is the address of my router.
My router also acts as a "caching DNS server" so I put in the address of the router here, as primary and my ISP's DNS server's IP address as the secondary.