stef25 wrote:
If my domain name is
www.stef.euYour domain is stef.eu in that case.
stef25 wrote:
what should the values in "hostname" and "aliases to" be? If I put "www" and "www.calamansi.eu" respectively, I get errors. Entering the IP of the server also produces errors.
Sorry, I'm very to new to all this

It sounds like you're trying to set up a CNAME. CNAME's are a special kind of DNS record that can't share their name with other records. If you have and A record for www you can't also have a CNAME for www. So you need to enter either an A record that points to the IP or a CNAME that points to a name which in turn points to the IP.
Does that make more sense?
-James