These may not answer all your questions, for further clarifications please contact us or open a support ticket.
The CertaSpace Nameservers are ns1.certa.space and ns2.certa.space.
Yes, you have to log into your Domain Registrar's client account and update your nameservers to ns1.certa.space and ns2.certa.space.
You can access your Cpanel by visiting your-domain-name.tld/cpanel where tld is either .com, .com.ng, .net, .edu.ng, .co, .org etc.
You can access your webmail by visiting your-domain-name.tld/webmail where tld is either .com, .com.ng, .net, .edu.ng, .co, .org etc.