1. web and web-skip
These two are used in case the IP on your interface (eth0 in your case) is not your external IP (your router is behind NAT). Then you put the address of some site that will give you your external IP (checkip.amazonaws.com or something). web-skip tells ddclient that the page returned at "web" has a bunch of junk before the IP and how much of it should be skipped.
I would delete what you have under "web" so they are both blank, unless you are behind NAT for some reason (maybe your ISP's modem has a built in router that you can't disable?). Then you would have Web = checkip.amazonaws.com and web-skip would still be blank.
2. Protocol: this should not be set to "-". Change it to dyndns2
3. how to tell if it's working
Once you've hit apply, ddclient will attempt to update dyndns automatically. Check the system log (in the GUI, click Toolbox in the top right corner, then log monitor) and there should be a message from ddclient beginning with SUCCESS or FAILED . If it fails it should tell you why.
4. more info
If you are wondering about the settings for ddclient (like why did I say use dyndns2 instead of dyndns1) check here