A Domain Name Registrar is an entity or corporation, such as netcup, that issues new domains by registering them with the ICANN.
Why should I use a certificate?
Using certificates has a wide range of advantages, as they provide you and your visitors with additional security and assurance that the information transferred between your server and their browser has not been altered in any way. Beyond that, every modern internet browser will display a warning message when trying to access a domain that does not have a properly issued certificate, making them indispensable for modern internet usage.