Check this if your ISP uses dynamic IP address assignment. That is your IP address will most likely change every time you establish a connection.
Check this is your ISP has given you a static IP address. In that case you will also need to fill in that address and any Subnet Mask if applicable. Ask your ISP if unsure.
Select this option if you want kppp to set the hostname and domain for your machine after successful setup of a ppp link on connect. This is done by querying the defined Domain Name Server with the ip assigned for the ppp link. This option is useful for those stand-alone machines which want to use protocols like talk which require the hostname to be the same as your machine is known in the Internet. It overrides the Domain Name Option in the DNS Section. The machine defaults are restored to the original values when you close the ppp link Be careful when choosing this option: It may prove useful to you, but it may also cause lots of undesired side effect. Just play with it ...