Create certificates with cert-issuer

I’m using coinbase and your wallet and I see so many addresses that I don’t know which ones to use, nor can I see my public and private keys.
Coinbase says it only gives out the public ones when you buy the bitcoin.
And the wallet only has public keys.
So where are they or how do I get the private key?
anyone knows which bitcoin portal was used at cert-issuer.

Thank you