domain name and host name

I'm generally new to Linux and am not sure if this is general or distro specific but I was wondering what these meant. They ask you to enter them (or something like it) as the first step of configuration of SuSE 10.1 when I chose the KDE interface. I'm not sure what they are or what to enter in these fields. And if so, can they be changed later?

I know what they are as internet terms (www.****.com and such)...
does this make your computer a server or something? so you can connect to it through internet?