As you are all most likely aware already all domain registrars ask for your personal information.
Such Personal Information Includes:
- Forename and Surname
- Address Information
- Email Address
- Telephone Number
Personal Information Via Whois
Depending on the domain type such as TLD or CCTLD this information may become immediately available after the registration of the domain via a simple whois. If you do not want that (and in most cases you certainly don't) they offer a service where you can remove this information from the whois service but of course hiding your personal information adds yearly costs to the domain purchase.
What Happens if I use Fake Details When Registering a Domain?