To enable networking, you have to select a primary interface (if your computer has several, this is the interface you're using to communicate with the local network). If you need several interfaces operating at once, you'll need to do advanced configuration, which is not covered by this tool. Anyhow, the usual primary interface is "eth0" on Linux and "hma0" on Solaris computers.
Next, you'll have to input a host IP. This is the unique address that identifies your computer on the network. Make sure no one is using this IP number already. Usual IPs for local networks are 10.10.10.*, where * represents any number in the range [1-254]. If you have a person acting as network administrator, you should probably ask her or him about this.
The netmask tells your computer which part of the IP number is static (i.e. equal for all computers on the network), where the remainder varies on a per-computer basis. A rule-of-thumb is that 255 in one of the fields means that this part of the IP is totally static, and 0 means it is totally dynamic. A common netmask is "255.255.255.0".
If your local network is connected to other networks, like the Internet, chances are you'll have a gateway. A gateway is a computer that relays information back and forth to other networks with other netmasks and IP ranges. Like any computer on the local network, the gateway also has an IP address. Enter it in the corresponding fields if you want to communicate with other networks.
You can tell your computer to enable networking (with the configuration you provide) every time it starts up. If your computer is a networked workstation, you'll generally want this.